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@ -0,0 +1,602 @@
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## Table of Contents
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## [<< Day 6](https://github.com/Asabeneh/30DaysOfJavaScript/blob/master/06_Day/06_day_loops.md) | [Day 7 >>](#)
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- [📔 Day 7](#%f0%9f%93%94-day-7)
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- [Functions](#functions)
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- [Function Declaration](#function-declaration)
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- [Function without a parameter and return](#function-without-a-parameter-and-return)
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- [Function returning value](#function-returning-value)
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- [Function with a parameter](#function-with-a-parameter)
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- [Function with two parameters](#function-with-two-parameters)
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- [Function with many parameters](#function-with-many-parameters)
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- [Function with unlimited number of parameters](#function-with-unlimited-number-of-parameters)
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- [Anonymous Function](#anonymous-function)
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- [Expression Function](#expression-function)
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- [Self Invoking Functions](#self-invoking-functions)
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- [Arrow Function](#arrow-function)
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- [Function with default parameters](#function-with-default-parameters)
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- [💻 Exercises](#%f0%9f%92%bb-exercises)
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# 📔 Day 7
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## Functions
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So far we have seen many builtin JavaScript functions. In this section, we will focus on custom functions. What is a function? Before we start making functions, lets understand what function is and why we need function?
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A function is a reusable block of code or programming statements designed to perform a certain task.
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A function is declared by a function key word followed by a name, followed by parentheses (). A parentheses can take a parameter. If a function take a parameter it will be called with argument. A function can also take a default parameter. To store a data to a function, a function has to return certain data types. To get the value we call or invoke a function.
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Function makes code:
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- clean and easy to read
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- reusable
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- easy to test
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A function can be declared or created in couple of ways:
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- _Declaration function_
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- _Expression function_
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- _Anonymous function_
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- _Arrow function_
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### Function Declaration
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Let us see how to declare a function and how to call a function.
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```js
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//declaring a function without a parameter
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function functionName() {
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// code goes here
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}
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functionName() // calling function by its name and with parentheses
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```
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#### Function without a parameter and return
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Function can be declared without a parameter.
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**Example:**
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```js
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// function without parameter, a function which square a number
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function square() {
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let num = 2
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let sq = num * num
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console.log(sq)
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}
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square() // 4
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// function without parameter
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function addTwoNumbers() {
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let numOne = 10
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let numTwo = 20
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let sum = numOne + numTwo
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console.log(sum)
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}
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addTwoNumbers() // function has to be called to be executed by it name
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```
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```js
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function generateFullName ():
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let firstName = 'Asabeneh'
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let lastName = 'Yetayeh'
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let space = ' '
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let fullName = firstName + space + lastName
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console.log(fullName)
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generateFullName() // calling a function
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```
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### Function returning value
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Function can also return values, if a function does not return values the value of the function is undefined. Let us write the above functions with return. From now on, we return value to a function instead of printing it.
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```js
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function generateFullName ():
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let firstName = 'Asabeneh'
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let lastName = 'Yetayeh'
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let space = ' '
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let fullName = firstName + space + lastName
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return fullName
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console.log(generateFullName())
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function addTwoNumbers {
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let numOne = 2
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let numTwo = 3
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let total = numOne + numTwo
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return total
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}
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console.log(addTwoNumbers())
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```
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#### Function with a parameter
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In a function we can pass different data types(number, string, boolean, object, function) as a parameter.
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```js
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// function with one parameter
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function functionName(parm1) {
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//code goes her
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}
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functionName(parm1) // during calling or invoking one argument needed
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function areaOfCircle(r) {
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let area = Math.PI * r * r
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return area
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}
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console.log(areaOfCircle(10)) // should be called with one argument
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function square(number) {
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return number * number
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}
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console.log(square(10))
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```
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#### Function with two parameters
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```js
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// function with two parameters
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function functionName(parm1, parm2) {
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//code goes her
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}
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functionName(parm1, parm2) // during calling or invoking two arguments needed
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// Function without parameter doesn't take input, so lets make a parameter with parameter
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function sumTwoNumbers(numOne, numTwo) {
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let sum = numOne + numTwo
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console.log(sum)
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}
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sumTwoNumbers(10, 20) // calling functions
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// If a function doesn't return it doesn't store data, so it should return
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function sumTwoNumbersAndReturn(numOne, numTwo) {
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let sum = numOne + numTwo
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return sum
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}
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console.log(sumTwoNumbersAndReturn(10, 20))
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function printFullName(firstName, lastName) {
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return `${firstName} ${lastName}`
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}
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console.log(printFullName('Asabeneh', 'Yetayeh'))
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```
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#### Function with many parameters
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```js
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// function with multiple parameters
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function functionName(parm1, parm2, parm3,...){
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//code goes here
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}
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functionName(parm1,parm2,parm3,...) // during calling or invoking three arguments needed
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// this function takes array as a parameter and sum up the numbers in the array
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function sumArrayValues(arr) {
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let sum = 0;
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for (let i = 0; i < arr.length; i++) {
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sum = sum + numbers[i];
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}
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return sum;
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}
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const numbers = [1, 2, 3, 4, 5];
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//calling a function
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console.log(sumArrayValues(numbers));
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const areaOfCircle = (radius) => {
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let area = Math.PI * radius * radius;
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return area;
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}
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console.log(areaOfCircle(10))
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```
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#### Function with unlimited number of parameters
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Sometimes we do not know how many arguments the user going to pass. Therefore, we should know how to write a function which can take unlimited number of arguments. A function declaration provides a function scoped arguments array like object. Any thing we passed as argument in the function can be access from arguments. Let us see an example
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```js
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// function declaration
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function sumAllNums() {
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let sum = 0
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for (let i = 0; i < arguments.length; i++) {
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sum = sum + arguments[i]
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}
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return sum
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}
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console.log(sumAllNums(1, 2, 3, 4)) // 10
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console.log(sumAllNums(10, 20, 13, 40, 10)) // 93
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console.log(sumAllNums(15, 20, 30, 25, 10, 33, 40)) // 173
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```
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### Anonymous Function
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Anonymous function or without name
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```js
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const anonymousFun = function() {
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console.log(
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'I am an anonymous function and my value is stored in anonymousFun'
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)
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}
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```
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### Expression Function
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Expression functions are anonymous functions. After we create a function without a name and with assign it to a variable. To return a value from the function we should call the variable. Look at the example below.
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```js
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//Declaration function
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function square(n) {
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return n * n
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}
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console.log(square(2)) // -> 4
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// Function expression
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const square = function(n) {
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return n * n
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}
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console.log(square(2)) // -> 4
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```
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### Self Invoking Functions
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Self invoking functions are anonymous functions which do not need to be called to return a value.
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```js
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;(function(n) {
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console.log(n * n)
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})(2) // 4, but instead of just printing if we want to return and store the data, we do as shown below
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let squaredNum = (function(n) {
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return n * n
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})(10)
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console.log(squaredNum)
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```
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### Arrow Function
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Arrow function is an alternative to write a function, however function declaration and arrow function have some minor differences.
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Arrow function uses arrow instead of the keyword function to declare a function. Let us see both function declaration and arrow function.
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```js
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// This is how we write normal or declaration function
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// Let us change this declaration function to an arrow function
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function square(n) {
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return n * n
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}
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console.log(square(2)) // 4
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const square = n => {
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return n * n
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}
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console.log(square(2)) // -> 4
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// if we have only one line, it can be written as follows, explicit return
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const square = n => n * n // -> 4
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```
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```js
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const changeToUpperCase = arr => {
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const newArr = []
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for (const element of arr) {
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newArr.push(element.toUpperCase())
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}
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return newArr
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}
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const countries = ['Finland', 'Sweden', 'Norway', 'Denmark', 'Iceland']
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console.log(changeToUpperCase(countries))
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// ["FINLAND", "SWEDEN", "NORWAY", "DENMARK", "ICELAND"]
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```
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```js
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const printFullName = (firstName, lastName) => {
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return `${firstName} ${lastName}`
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}
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console.log(printFullName('Asabeneh', 'Yetayeh'))
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```
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The above function has only the return statement, therefore, we can explicitly return it as follows.
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```js
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const printFullName = (firstName, lastName) => {
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return `${firstName} ${lastName}`
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}
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console.log(printFullName('Asabeneh', 'Yetayeh'))
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```
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### Function with default parameters
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Sometimes we pass default values to parameters, when we invoke the function if we do not pass an argument the default value will be used. Both function declaration and arrow function can have a default value or values.
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```js
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// syntax
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// Declaring a function
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function functionName(param = value) {
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//codes
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}
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// Calling function
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functionName()
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functionName(arg)
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```
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**Example:**
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```js
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function greetings(name = 'Peter') {
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let message = `${name}, welcome to 30 Days Of JavaScript!`
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return message
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}
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console.log(greetings())
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console.log(greetings('Asabeneh'))
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```
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```js
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function generateFullName(firstName = 'Asabeneh', lastName = 'Yetayeh') {
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let space = ' '
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let fullName = firstName + space + lastName
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return fullName
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|
}
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console.log(generateFullName())
|
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|
console.log(generateFullName('David', 'Smith'))
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|
```
|
|
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|
|
|
|
|
```js
|
|
|
|
|
function calculate_age(birthYear, currentYear = 2019) {
|
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|
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|
let age = currentYear - birthYear
|
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|
return age
|
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|
|
}
|
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|
console.log('Age: ', calculateAge(1819))
|
|
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|
|
```
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|
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|
|
```js
|
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|
|
function weightOfObject(mass, gravity = 9.81) {
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|
let weight = mass * gravity + ' N' // the value has to be changed to string first
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|
return weight
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|
}
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|
|
console.log('Weight of an object in Newton: ', weightOfObject(100)) // 9.81 gravity at the surface of Earth
|
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|
console.log('Weight of an object in Newton: ', weightOfObject(100, 1.62)) // gravity at surface of Moon
|
|
|
|
|
```
|
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|
|
|
|
|
Let us see how we write the above functions with arrow functions
|
|
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|
|
|
|
|
|
|
```js
|
|
|
|
|
// syntax
|
|
|
|
|
// Declaring a function
|
|
|
|
|
const functionName = (param = value) => {
|
|
|
|
|
//codes
|
|
|
|
|
}
|
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|
|
|
|
|
|
|
// Calling function
|
|
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|
functionName()
|
|
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|
|
functionName(arg)
|
|
|
|
|
```
|
|
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|
|
|
|
|
|
**Example:**
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
const greetings = (name = 'Peter') => {
|
|
|
|
|
let message = name + ', welcome to 30 Days Of JavaScript!'
|
|
|
|
|
return message
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
console.log(greetings())
|
|
|
|
|
console.log(greetings('Asabeneh'))
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
const generateFullName = (firstName = 'Asabeneh', lastName = 'Yetayeh') => {
|
|
|
|
|
let space = ' '
|
|
|
|
|
let fullName = firstName + space + lastName
|
|
|
|
|
return fullName
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
console.log(generateFullName())
|
|
|
|
|
console.log(generateFullName('David', 'Smith'))
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
|
|
|
|
|
const calculateAge = (birthYear, currentYear = 2019) => currentYear - birthYear
|
|
|
|
|
console.log('Age: ', calculateAge(1819))
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
const weightOfObject = (mass, gravity = 9.81) => mass * gravity + ' N'
|
|
|
|
|
|
|
|
|
|
console.log('Weight of an object in Newton: ', weightOfObject(100)) // 9.81 gravity at the surface of Earth
|
|
|
|
|
console.log('Weight of an object in Newton: ', weightOfObject(100, 1.62)) // gravity at surface of Moon
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
🌕 You are a rising stat, now you knew function . Now, you are super charged with the power of functions. You have just completed day 6 challenges and you are 6 steps a head in to your way to greatness. Now do some exercises for your brain and for your muscle.
|
|
|
|
|
|
|
|
|
|
## 💻 Exercises
|
|
|
|
|
|
|
|
|
|
1. Declare a function _fullName_ and it print out your full name.
|
|
|
|
|
2. Declare a function _fullName_ and now it takes firstName, lastName as a parameter and it returns your full - name.
|
|
|
|
|
3. Declare a function _addNumbers_ and it takes two two parameters and it returns sum.
|
|
|
|
|
4. An area of a rectangle is calculated as follows: _area = length x width_. Write a function which calculates _areaOfRectangle_.
|
|
|
|
|
5. A perimeter of a rectangle is calculated as follows: _perimeter= 2x(length + width)_. Write a function which calculates _perimeterOfRectangle_.
|
|
|
|
|
6. A volume of a rectangular prism is calculated as follows: _volume = length x width x height_. Write a function which calculates _volumeOfRectPrism_.
|
|
|
|
|
7. Area of a circle is calculated as follows: _area = π x r x r_. Write a function which calculates _areaOfCircle_
|
|
|
|
|
8. Circumference of a circle is calculated as follows: _circumference = 2πr_. Write a function which calculates _circumOfCircle_
|
|
|
|
|
9. Density of a substance is calculated as follows:_density= mass/volume_. Write a function which calculates _density_.
|
|
|
|
|
10. Speed is calculated by dividing the total distance covered by a moving object divided by the total amount of time taken. Write a function which calculates a speed of a moving object, _speed_.
|
|
|
|
|
11. Weight of a substance is calculated as follows: _weight = mass x gravity_. Write a function which calculates _weight_.
|
|
|
|
|
12. Temperature in oC can be converted to oF using this formula: _oF = (oC x 9/5) + 32_. Write a function which convert oC to oF _convertCelciusToFahrenheit_.
|
|
|
|
|
13. Body mass index(BMI) is calculated as follows: _bmi = weight in Kg / (height x height) in m2_. Write a function which calculates _bmi_. BMI is used to broadly define different weight groups in adults 20 years old or older.Check if a person is _underweight, normal, overweight_ or _obese_ based the information given below.
|
|
|
|
|
|
|
|
|
|
- The same groups apply to both men and women.
|
|
|
|
|
- _Underweight_: BMI is less than 18.5
|
|
|
|
|
- _Normal weight_: BMI is 18.5 to 24.9
|
|
|
|
|
- _Overweight_: BMI is 25 to 29.9
|
|
|
|
|
- _Obese_: BMI is 30 or more
|
|
|
|
|
|
|
|
|
|
14. Write a function called _checkSeason_, it takes a month parameter and returns the season:Autumn, Winter, Spring or Summer.
|
|
|
|
|
15. Math.max returns its largest argument. Write a function findMax that takes three arguments and returns their maximum with out using Math.max method.
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
console.log(findMax(0, 10, 5))
|
|
|
|
|
10
|
|
|
|
|
console.log(findMax(0, -10, -2))
|
|
|
|
|
0
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
16. Linear equation is calculated as follows: _ax + by + c = 0_. Write a function which calculates value of a linear equation, _solveLinEquation_.
|
|
|
|
|
17. Quadratic equation is calculated as follows: _ax2 + bx + c = 0_. Write a function which calculates value or values of a quadratic equation, _solveQuadEquation_.
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
console.log(solveQuadratic()) // {0}
|
|
|
|
|
console.log(solveQuadratic(1, 4, 4)) // {-2}
|
|
|
|
|
console.log(solveQuadratic(1, -1, -2)) // {2, -1}
|
|
|
|
|
console.log(solveQuadratic(1, 7, 12)) // {-3, -4}
|
|
|
|
|
console.log(solveQuadratic(1, 0, -4)) //{2, -2}
|
|
|
|
|
console.log(solveQuadratic(1, -1, 0)) //{1, 0}
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
18. Declare a function name _printArray_. It takes array as a parameter and it prints out each value of the array.
|
|
|
|
|
19. Declare a function name _swapValues_. This function swaps value of x to y.
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
swapValues(3, 4) // x => 4, y=>3
|
|
|
|
|
swapValues(4, 5) // x = 5, y = 4
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
20. Declare a function name _reverseArray_. It takes array as a parameter and it returns the reverse of the array (don't use method).
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
console.log(reverseArray([1, 2, 3, 4, 5]))
|
|
|
|
|
//[5, 4, 3, 2, 1]
|
|
|
|
|
console.log(reverseArray(['A', 'B', 'C']))
|
|
|
|
|
//['C', 'B', 'A']
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
21. Declare a function name _capitalizeArray_. It takes array as a parameter and it returns the - capitalizedarray.
|
|
|
|
|
22. Declare a function name _addItem_. It takes an item parameter and it returns an array after adding the item
|
|
|
|
|
23. Declare a function name _removeItem_. It takes an index parameter and it returns an array after removing an item
|
|
|
|
|
24. Declare a function name _sumOfNumbers_. It takes a number parameter and it adds all the numbers in that range.
|
|
|
|
|
25. Declare a function name _sumOfOdds_. It takes a number parameter and it adds all the odd numbers in that - range.
|
|
|
|
|
26. Declare a function name _sumOfEven_. It takes a number parameter and it adds all the even numbers in that - range.
|
|
|
|
|
27. Declare a function name evensAndOdds . It takes a positive integer as parameter and it counts number of evens and odds in the number.
|
|
|
|
|
|
|
|
|
|
```sh
|
|
|
|
|
evensAndOdds(100);
|
|
|
|
|
The number of odds are 50.
|
|
|
|
|
The number of evens are 51.
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
28. Write a function which takes any number of arguments and return the sum of the arguments
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
sum(1, 2, 3) // -> 6
|
|
|
|
|
sum(1, 2, 3, 4) // -> 10
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
29. Writ a function which generates a _randomUserIp_.
|
|
|
|
|
30. Write a function which generates a _randomMacAddress_
|
|
|
|
|
31. Declare a function name _randomHexaNumberGenerator_. When this function is called it generates a random hexadecimal number. The function return the hexadecimal number.
|
|
|
|
|
|
|
|
|
|
```sh
|
|
|
|
|
console.log(randomHexaNumberGenerator());
|
|
|
|
|
'#ee33df'
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
32. Declare a function name _userIdGenerator_. When this function is called it generates seven character id. The function return the id.
|
|
|
|
|
|
|
|
|
|
```sh
|
|
|
|
|
console.log(userIdGenerator());
|
|
|
|
|
41XTDbE
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
33. Modify question number n . Declare a function name _userIdGeneratedByUser_. It doesn’t take any parameter but it takes two inputs using prompt(). One of the input is the number of characters and the second input is the number of ids which are supposed to be generated.
|
|
|
|
|
|
|
|
|
|
```sh
|
|
|
|
|
userIdGeneratedByUser()
|
|
|
|
|
'kcsy2
|
|
|
|
|
SMFYb
|
|
|
|
|
bWmeq
|
|
|
|
|
ZXOYh
|
|
|
|
|
2Rgxf
|
|
|
|
|
'
|
|
|
|
|
userIdGeneratedByUser()
|
|
|
|
|
'1GCSgPLMaBAVQZ26
|
|
|
|
|
YD7eFwNQKNs7qXaT
|
|
|
|
|
ycArC5yrRupyG00S
|
|
|
|
|
UbGxOFI7UXSWAyKN
|
|
|
|
|
dIV0SSUTgAdKwStr
|
|
|
|
|
'
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
34. Write a function name _rgbColorGenerator_ and it generates rgb colors.
|
|
|
|
|
|
|
|
|
|
```sh
|
|
|
|
|
rgbColorGenerator()
|
|
|
|
|
rgb(125,244,255)
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
35. Write a function **_arrayOfHexaColors_** which return any number of hexadecimal colors in an array.
|
|
|
|
|
36. Write a function **_arrayOfRgbColors_** which return any number of RGB colors in an array.
|
|
|
|
|
37. Write a function **_convertHexaToRgb_** which converts hexa color to rgb and it returns an rgb color.
|
|
|
|
|
38. Write a function **_convertRgbToHexa_** which converts rgb to hexa color and it returns an hexa color.
|
|
|
|
|
39. Write a function **_generateColors_** which can generate any number of hexa or rgb colors.
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
console.log(generateColors('hexa', 3)) // ['#a3e12f', '#03ed55', '#eb3d2b']
|
|
|
|
|
console.log(generateColors('hexa', 1)) // '#b334ef'
|
|
|
|
|
console.log(generateColors('rgb', 3)) // ['rgb(5, 55, 175)', 'rgb(50, 105, 100)', 'rgb(15, 26, 80)']
|
|
|
|
|
console.log(generateColors('rgb', 1)) // 'rgb(33,79, 176)'
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
40. Call your function _shuffleArray_, it takes an array as a parameter and it returns a shuffled array
|
|
|
|
|
41. Call your function _factorial_, it takes a whole number as a parameter and it return a factorial of the number
|
|
|
|
|
42. Call your function _isEmpty_, it takes a parameter and it checks if it is empty or not
|
|
|
|
|
43. Call your function _sum_, it takes any number of arguments and it returns the sum.
|
|
|
|
|
44. Write a function called _sumOfArrayItems_, it takes an array parameter and return the sum of all the items. Check if all the array items are number types. If not give return reasonable feedback.
|
|
|
|
|
45. Write a function called _average_, it takes an array parameter and returns the average of the items. Check if all the array items are number types. If not give return reasonable feedback.
|
|
|
|
|
46. Write a function called _modifyArray_ takes array as parameter and modifies the fifth item of the array and return the array. If the array length is less than five it return 'item not found'.
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
console.log(modifyArray(['Avocado', 'Tomato', 'Potato','Mango', 'Lemon','Carrot']);
|
|
|
|
|
// →['Avocado', 'Tomato', 'Potato','Mango', 'LEMON', 'Carrot']
|
|
|
|
|
console.log(modifyArray(['Google', 'Facebook','Apple', 'Amazon','Microsoft', 'IBM']);
|
|
|
|
|
// →['Google', 'Facebook','Apple', 'Amazon','MICROSOFT', 'IBM']
|
|
|
|
|
console.log(modifyArray(['Google', 'Facebook','Apple', 'Amazon']);
|
|
|
|
|
// →'Not Found'
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
47. Write a function called _isPrime_, which checks if a number is prime number.
|
|
|
|
|
48. Write a functions which checks if all items are unique in the array.
|
|
|
|
|
49. Write a function which checks if all the items of the array are the same data type.
|
|
|
|
|
50. JavaScript variable name does not support special characters or symbols except \$ or \_. Write a function **\*isValidVariable** which check if a variable is valid or invalid variable.
|
|
|
|
|
51. Write a function which returns array of seven random numbers in a range of 0-9. All the numbers must be unique.
|
|
|
|
|
|
|
|
|
|
```js
|
|
|
|
|
sevenRandomNumbers()[(1, 4, 5, 7, 9, 8, 0)]
|
|
|
|
|
```
|
|
|
|
|
|
|
|
|
|
52. Write a function called reverseCountries, it takes countries array and first it copy the array and returns the reverse of the original array
|
|
|
|
|
|
|
|
|
|
🎉 CONGRATULATIONS ! 🎉
|
|
|
|
|
|
|
|
|
|
[<< Day 6](https://github.com/Asabeneh/30DaysOfJavaScript/blob/master/06_Day/06_day_loops.md) | [Day 7 >>](#)
|
Asabeneh
5 years ago