From ac36e2f8b80e8e5e74b82c52436ab558abec7cd0 Mon Sep 17 00:00:00 2001
From: Abhishek765 <vishwakarmaabhishek31@gmail.com>
Date: Sun, 2 Oct 2022 01:24:59 +0530
Subject: [PATCH] feat: Added some JS polyfills

---
 10-Js-polyfills/Promise.js    | 67 +++++++++++++++++++++++++++++++++++
 10-Js-polyfills/PromiseAll.js | 58 ++++++++++++++++++++++++++++++
 10-Js-polyfills/myFilter.js   | 19 ++++++++++
 10-Js-polyfills/myMap.js      | 17 +++++++++
 10-Js-polyfills/myReduce.js   | 18 ++++++++++
 5 files changed, 179 insertions(+)
 create mode 100644 10-Js-polyfills/Promise.js
 create mode 100644 10-Js-polyfills/PromiseAll.js
 create mode 100644 10-Js-polyfills/myFilter.js
 create mode 100644 10-Js-polyfills/myMap.js
 create mode 100644 10-Js-polyfills/myReduce.js

diff --git a/10-Js-polyfills/Promise.js b/10-Js-polyfills/Promise.js
new file mode 100644
index 00000000..33299324
--- /dev/null
+++ b/10-Js-polyfills/Promise.js
@@ -0,0 +1,67 @@
+function myPromise(executer) {
+  let onResolve,
+    onReject,
+    isFullFilled = false,
+    isCalled = false,
+    value;
+
+  this.then = function (callback) {
+    onResolve = callback;
+
+    if (isFullFilled && !isCalled) {
+      isCalled = true;
+      onResolve(value);
+    }
+    return this;
+  };
+
+  this.catch = function (callback) {
+    onReject = callback;
+    if (isFullFilled && !isCalled) {
+      isCalled = true;
+      onReject(value);
+    }
+    return this;
+  };
+
+  function resolve(val) {
+    isFullFilled = true;
+    value = val;
+    if (typeof onResolve === "function") {
+      isCalled = true;
+      onResolve(val);
+    }
+  }
+
+  function reject(val) {
+    isFullFilled = true;
+    value = val;
+    if (typeof onReject === "function") {
+      isCalled = true;
+      onReject(val);
+    }
+  }
+
+  // Error handling for  executer
+  try {
+    executer(resolve, reject);
+  } catch (error) {
+    reject(error);
+  }
+}
+
+const examplePromise = new myPromise((resolve, reject) => {
+  let state = false;
+  setTimeout(() => {
+    if (state) resolve("Promise resolved");
+    else reject("Promise rejected");
+  }, 1000);
+});
+
+examplePromise
+  .then((res) => {
+    console.log(res);
+  })
+  .catch((err) => {
+    throw new Error(err);
+  });
diff --git a/10-Js-polyfills/PromiseAll.js b/10-Js-polyfills/PromiseAll.js
new file mode 100644
index 00000000..2f10b118
--- /dev/null
+++ b/10-Js-polyfills/PromiseAll.js
@@ -0,0 +1,58 @@
+// Resolved promise
+function promise1(val) {
+  return new Promise((resolve, reject) => {
+    setTimeout(() => {
+      resolve(val);
+    }, 1000);
+  });
+}
+
+// Rejected promise
+function promise2(val) {
+  return new Promise((resolve, reject) => {
+    setTimeout(() => {
+      reject(val);
+    }, 1000);
+  });
+}
+
+// Resolved promise
+function promise3(val) {
+  return new Promise((resolve, reject) => {
+    setTimeout(() => {
+      resolve(val);
+    }, 1000);
+  });
+}
+
+Promise.myAllPromise = (promises) => {
+  return new Promise((resolve, reject) => {
+    let results = [];
+
+    if (promises.length === 0) {
+      resolve(results);
+      return;
+    }
+
+    let promisePendingState = promises.length;
+
+    promises.forEach((promise, index) => {
+      Promise.resolve(promise).then((res) => {
+        results[index] = res;
+        promisePendingState--;
+
+        if (promisePendingState === 0) {
+          resolve(results);
+        }
+      }, reject);
+    });
+  });
+};
+
+Promise.myAllPromise([
+  promise1("hello from promise 1"),
+  promise2("hello from promise 2"),
+  promise3("hello from promise 3"),
+])
+  .then((res) => console.log(res))
+  .catch((err) => console.error(`failed Promise: ${err}`));
diff --git a/10-Js-polyfills/myFilter.js b/10-Js-polyfills/myFilter.js
new file mode 100644
index 00000000..08a9b2dc
--- /dev/null
+++ b/10-Js-polyfills/myFilter.js
@@ -0,0 +1,19 @@
+const numbers = [1, 2, 3, 4, 5];
+// structure -> Array.filter((ele, index, arr) => {})
+
+Array.prototype.myFilter = function (callback) {
+  let newArr = [];
+
+  for (let i = 0; i < this.length; i++) {
+    if (callback(this[i], i, this)) {
+      newArr.push(this[i]);
+    }
+  }
+
+  return newArr;
+};
+
+// const filteredNumbers = numbers.filter((num) => num > 2);
+const filteredNumbers = numbers.myFilter((num) => num > 2);
+
+console.log({ filteredNumbers });
diff --git a/10-Js-polyfills/myMap.js b/10-Js-polyfills/myMap.js
new file mode 100644
index 00000000..7f4baf98
--- /dev/null
+++ b/10-Js-polyfills/myMap.js
@@ -0,0 +1,17 @@
+const numbers = [1, 2, 3, 4, 5];
+// structure -> Array.map((ele, index, arr) => {})
+
+Array.prototype.myMap = function (callback) {
+  let newArr = [];
+
+  for (let i = 0; i < this.length; i++) {
+    newArr.push(callback(this[i], i, this));
+  }
+
+  return newArr;
+};
+
+// const modifiedNumbers = numbers.map((num) => num * 2);
+const modifiedNumbers = numbers.myMap((num) => num * 2);
+
+console.log({ modifiedNumbers });
diff --git a/10-Js-polyfills/myReduce.js b/10-Js-polyfills/myReduce.js
new file mode 100644
index 00000000..ef83a730
--- /dev/null
+++ b/10-Js-polyfills/myReduce.js
@@ -0,0 +1,18 @@
+const numbers = [1, 2, 3, 4, 5];
+// structure -> Array.reduce((acc, curr, index, arr) => {}, initialValue)
+
+Array.prototype.myReduce = function (callback, initialValue) {
+  let accumulator = initialValue;
+
+  // after assigning initialValue to accumulator we need to check whether accumulator exists or not
+  for (let i = 0; i < this.length; i++) {
+    accumulator = accumulator ? accumulator + this[i] : this[i];
+  }
+
+  return accumulator;
+};
+
+// const sum = numbers.reduce((acc, curr) => acc + curr, 0);
+const sum = numbers.myReduce((acc, curr) => acc + curr, 0);
+
+console.log({ sum });