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---
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title: API reference
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---
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## TODO MAKE THIS CURRENT, INCLUDE svelte, svelte/store, ETC ETC
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As we saw above, you create a component instance with the `new` keyword:
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```js
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/* { filename: 'main.js' } */
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import App from './App.html';
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const component = new App({
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// `target` is the only required option. This is the
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// DOM element your component will be appended to
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target: document.querySelector('main'),
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// `anchor` is optional.
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// The component is inserted immediately before this
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// DOM element, which must be a child of `target`
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anchor: document.querySelector('main #child'),
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// `props` is optional. A component can also have
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// default props – we'll learn about that later.
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props: {
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questions: [
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'life',
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'the universe',
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'everything'
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],
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answer: 42
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}
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});
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```
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Normally, you'd interact with a component by getting and setting *props*:
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```js
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console.log(component.answer); // 42
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component.answer = 420;
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```
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Every Svelte component instance has three built-in methods:
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### component.$set(props)
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This updates the component's state with the new values provided and causes the DOM to update. `state` must be a plain old JavaScript object (POJO). Any properties *not* included in `state` will remain as they were.
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```js
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component.set({
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questions: [
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'why is the sky blue?',
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'how do planes fly?',
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'where do babies come from?'
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],
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answer: 'ask your mother'
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});
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```
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### component.get()
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Returns the component's current state:
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```js
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const { questions, answer } = component.get();
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console.log(answer); // 'ask your mother'
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```
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This will also retrieve the value of [computed properties](guide#computed-properties).
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> Previous versions of Svelte allowed you to specify a key to retrieve a specific value — this was removed in version 2.
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### component.on(eventName, callback)
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Allows you to respond to *events*:
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```js
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const listener = component.on('thingHappened', event => {
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console.log(`A thing happened: ${event.thing}`);
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});
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// some time later...
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listener.cancel();
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```
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Each component has three built-in events, corresponding to their [lifecycle hooks](guide#lifecycle-hooks):
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```js
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component.on('state', ({ changed, current, previous }) => {
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console.log('state changed', current);
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});
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component.on('update', ({ changed, current, previous }) => {
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console.log('DOM updated after state change', current);
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});
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component.on('destroy', () => {
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console.log('this component is being destroyed');
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});
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```
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### component.fire(eventName, event)
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The companion to `component.on(...)`:
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```js
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component.fire('thingHappened', {
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thing: 'this event was fired'
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});
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```
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At first glance `component.on(...)` and `component.fire(...)` aren't particularly useful, but it'll become more so when we learn about [nested components](guide#nested-components) and [component events](guide#component-events).
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### component.destroy()
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Removes the component from the DOM and removes any event listeners that were created. This will also fire a `destroy` event:
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```js
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component.on('destroy', () => {
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alert('goodbye!'); // please don't do this
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});
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component.destroy();
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```
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### component.options
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The options used to instantiate the component are available in `component.options`.
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```html
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<!-- { title: 'component.options' } -->
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Check the console.
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<script>
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export default {
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oncreate() {
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console.log(this.options);
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}
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};
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</script>
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```
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This gives you access to standard options like `target` and `data`, but can also be used to access any other custom options you may choose to implement for your component.
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### component.root
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In [nested components](guide#nested-components), each component has a `root` property pointing to the top-level root component – that is, the one instantiated with `new MyComponent({...})`.
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> Earlier versions of Svelte had a `component.observe(...)` method. This was removed in version 2, in favour of the `onstate` [lifecycle hook](guide#lifecycle-hooks), but is still available via [svelte-extras](https://github.com/sveltejs/svelte-extras).
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