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294 lines
8.7 KiB
294 lines
8.7 KiB
# event-target-shim
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[](https://www.npmjs.com/package/event-target-shim)
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[](http://www.npmtrends.com/event-target-shim)
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[](https://travis-ci.org/mysticatea/event-target-shim)
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[](https://codecov.io/gh/mysticatea/event-target-shim)
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[](https://david-dm.org/mysticatea/event-target-shim)
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An implementation of [WHATWG EventTarget interface](https://dom.spec.whatwg.org/#interface-eventtarget), plus few extensions.
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- This provides `EventTarget` constructor that can inherit for your custom object.
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- This provides an utility that defines properties of attribute listeners (e.g. `obj.onclick`).
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```js
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import {EventTarget, defineEventAttribute} from "event-target-shim"
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class Foo extends EventTarget {
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// ...
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}
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// Define `foo.onhello` property.
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defineEventAttribute(Foo.prototype, "hello")
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// Use
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const foo = new Foo()
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foo.addEventListener("hello", e => console.log("hello", e))
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foo.onhello = e => console.log("onhello:", e)
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foo.dispatchEvent(new CustomEvent("hello"))
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```
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## 💿 Installation
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Use [npm](https://www.npmjs.com/) to install then use a bundler.
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```
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npm install event-target-shim
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```
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Or download from [`dist` directory](./dist).
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- [dist/event-target-shim.mjs](dist/event-target-shim.mjs) ... ES modules version.
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- [dist/event-target-shim.js](dist/event-target-shim.js) ... Common JS version.
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- [dist/event-target-shim.umd.js](dist/event-target-shim.umd.js) ... UMD (Universal Module Definition) version. This is transpiled by [Babel](https://babeljs.io/) for IE 11.
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## 📖 Usage
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```js
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import {EventTarget, defineEventAttribute} from "event-target-shim"
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// or
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const {EventTarget, defineEventAttribute} = require("event-target-shim")
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// or UMD version defines a global variable:
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const {EventTarget, defineEventAttribute} = window.EventTargetShim
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```
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### EventTarget
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> https://dom.spec.whatwg.org/#interface-eventtarget
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#### eventTarget.addEventListener(type, callback, options)
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Register an event listener.
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- `type` is a string. This is the event name to register.
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- `callback` is a function. This is the event listener to register.
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- `options` is a boolean or an object `{ capture?: boolean, passive?: boolean, once?: boolean }`. If this is a boolean, it's same meaning as `{ capture: options }`.
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- `capture` is the flag to register the event listener for capture phase.
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- `passive` is the flag to ignore `event.preventDefault()` method in the event listener.
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- `once` is the flag to remove the event listener automatically after the first call.
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#### eventTarget.removeEventListener(type, callback, options)
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Unregister an event listener.
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- `type` is a string. This is the event name to unregister.
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- `callback` is a function. This is the event listener to unregister.
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- `options` is a boolean or an object `{ capture?: boolean }`. If this is a boolean, it's same meaning as `{ capture: options }`.
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- `capture` is the flag to register the event listener for capture phase.
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#### eventTarget.dispatchEvent(event)
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Dispatch an event.
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- `event` is a [Event](https://dom.spec.whatwg.org/#event) object or an object `{ type: string, [key: string]: any }`. The latter is non-standard but useful. In both cases, listeners receive the event as implementing [Event](https://dom.spec.whatwg.org/#event) interface.
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### defineEventAttribute(proto, type)
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Define an event attribute (e.g. `onclick`) to `proto`. This is non-standard.
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- `proto` is an object (assuming it's a prototype object). This function defines a getter/setter pair for the event attribute.
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- `type` is a string. This is the event name to define.
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For example:
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```js
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class AbortSignal extends EventTarget {
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constructor() {
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this.aborted = false
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}
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}
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// Define `onabort` property.
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defineEventAttribute(AbortSignal.prototype, "abort")
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```
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### EventTarget(types)
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Define a custom `EventTarget` class with event attributes. This is non-standard.
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- `types` is a string or an array of strings. This is the event name to define.
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For example:
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```js
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// This has `onabort` property.
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class AbortSignal extends EventTarget("abort") {
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constructor() {
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this.aborted = false
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}
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}
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```
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## 📚 Examples
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### ES2015 and later
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> https://jsfiddle.net/636vea92/
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```js
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const {EventTarget, defineEventAttribute} = EventTargetShim
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// Define a derived class.
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class Foo extends EventTarget {
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// ...
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}
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// Define `foo.onhello` property.
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defineEventAttribute(Foo.prototype, "hello")
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// Register event listeners.
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const foo = new Foo()
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foo.addEventListener("hello", (e) => {
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console.log("hello", e)
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})
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foo.onhello = (e) => {
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console.log("onhello", e)
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}
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// Dispatching events
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foo.dispatchEvent(new CustomEvent("hello", { detail: "detail" }))
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```
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### Typescript
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```ts
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import { EventTarget, defineEventAttribute } from "event-target-shim";
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// Define events
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type FooEvents = {
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hello: CustomEvent
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}
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type FooEventAttributes = {
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onhello: CustomEvent
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}
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// Define a derived class.
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class Foo extends EventTarget<FooEvents, FooEventAttributes> {
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// ...
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}
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// Define `foo.onhello` property's implementation.
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defineEventAttribute(Foo.prototype, "hello")
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// Register event listeners.
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const foo = new Foo()
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foo.addEventListener("hello", (e) => {
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console.log("hello", e.detail)
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})
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foo.onhello = (e) => {
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console.log("onhello", e.detail)
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}
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// Dispatching events
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foo.dispatchEvent(new CustomEvent("hello", { detail: "detail" }))
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```
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Unfortunately, both `FooEvents` and `FooEventAttributes` are needed because TypeScript doesn't allow the mutation of string literal types. If TypeScript allowed us to compute `"onhello"` from `"hello"` in types, `FooEventAttributes` will be optional.
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This `EventTarget` type is compatible with `EventTarget` interface of `lib.dom.d.ts`.
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#### To disallow unknown events
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By default, methods such as `addEventListener` accept unknown events. You can disallow unknown events by the third type parameter `"strict"`.
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```ts
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type FooEvents = {
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hello: CustomEvent
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}
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class Foo extends EventTarget<FooEvents, {}, "strict"> {
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// ...
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}
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// OK because `hello` is defined in FooEvents.
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foo.addEventListener("hello", (e) => {
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})
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// Error because `unknown` is not defined in FooEvents.
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foo.addEventListener("unknown", (e) => {
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})
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```
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However, if you use `"strict"` parameter, it loses compatibility with `EventTarget` interface of `lib.dom.d.ts`.
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#### To infer the type of `dispatchEvent()` method
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TypeScript cannot infer the event type of `dispatchEvent()` method properly from the argument in most cases. You can improve this behavior with the following steps:
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1. Use the third type parameter `"strict"`. This prevents inferring to `dispatchEvent<string>()`.
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2. Make the `type` property of event definitions stricter.
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```ts
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type FooEvents = {
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hello: CustomEvent & { type: "hello" }
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hey: Event & { type: "hey" }
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}
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class Foo extends EventTarget<FooEvents, {}, "strict"> {
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// ...
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}
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// Error because `detail` property is lacking.
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foo.dispatchEvent({ type: "hello" })
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```
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### ES5
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> https://jsfiddle.net/522zc9de/
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```js
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// Define a derived class.
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function Foo() {
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EventTarget.call(this)
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}
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Foo.prototype = Object.create(EventTarget.prototype, {
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constructor: { value: Foo, configurable: true, writable: true }
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// ...
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})
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// Define `foo.onhello` property.
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defineEventAttribute(Foo.prototype, "hello")
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// Register event listeners.
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var foo = new Foo()
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foo.addEventListener("hello", function(e) {
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console.log("hello", e)
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})
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foo.onhello = function(e) {
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console.log("onhello", e)
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}
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// Dispatching events
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function isSupportEventConstrucor() { // IE does not support.
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try {
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new CusomEvent("hello")
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return true
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} catch (_err) {
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return false
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}
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}
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if (isSupportEventConstrucor()) {
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foo.dispatchEvent(new CustomEvent("hello", { detail: "detail" }))
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} else {
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var e = document.createEvent("CustomEvent")
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e.initCustomEvent("hello", false, false, "detail")
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foo.dispatchEvent(e)
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}
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```
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## 📰 Changelog
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- See [GitHub releases](https://github.com/mysticatea/event-target-shim/releases).
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## 🍻 Contributing
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Contributing is welcome ❤️
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Please use GitHub issues/PRs.
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### Development tools
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- `npm install` installs dependencies for development.
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- `npm test` runs tests and measures code coverage.
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- `npm run clean` removes temporary files of tests.
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- `npm run coverage` opens code coverage of the previous test with your default browser.
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- `npm run lint` runs ESLint.
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- `npm run build` generates `dist` codes.
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- `npm run watch` runs tests on each file change.
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