54 lines
1.6 KiB
Markdown
54 lines
1.6 KiB
Markdown
### runAsync
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Runs a function in a separate thread by using a Web Worker, allowing
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long running functions to not block the UI.
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Create a new `Worker` using a `Blob` object URL, the contents of which should be the
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stringified version of the supplied function. Immediately post the return value of calling
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the function back. Return a promise, listening for `onmessage` and `onerror` events
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and resolving the data posted back from the worker, or throwing an error.
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```js
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const runAsync = fn => {
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const blob = `
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var fn = ${fn.toString()};
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this.postMessage(fn());
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`;
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const worker = new Worker(
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URL.createObjectURL(new Blob([blob]), {
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type: 'application/javascript; charset=utf-8'
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})
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);
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return new Promise((res, rej) => {
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worker.onmessage = ({ data }) => {
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res(data), worker.terminate();
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};
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worker.onerror = err => {
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rej(err), worker.terminate();
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};
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});
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};
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```
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```js
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const longRunningFunction = () => {
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let result = 0;
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for (var i = 0; i < 1000; i++) {
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for (var j = 0; j < 700; j++) {
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for (var k = 0; k < 300; k++) {
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result = result + i + j + k;
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}
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}
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}
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return result;
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};
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// NOTE: Since the function is running in a different context, closures are not supported.
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// The function supplied to `runAsync` gets stringified, so everything becomes literal.
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// All variables and functions must be defined inside.
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runAsync(longRunningFunction).then(console.log); // 209685000000
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runAsync(() => 10 ** 3).then(console.log); // 1000
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let outsideVariable = 50;
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runAsync(() => typeof outsideVariable).then(console.log); // 'undefined'
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```
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