196 lines
4.9 KiB
Markdown
196 lines
4.9 KiB
Markdown
# JavaScript Sync/Async forEach
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An optionally-asynchronous forEach with an interesting interface.
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## Getting Started
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This code should work just fine in Node.js:
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First, install the module with: `npm install async-foreach`
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```javascript
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var forEach = require('async-foreach').forEach;
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forEach(["a", "b", "c"], function(item, index, arr) {
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console.log("each", item, index, arr);
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});
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// logs:
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// each a 0 ["a", "b", "c"]
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// each b 1 ["a", "b", "c"]
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// each c 2 ["a", "b", "c"]
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```
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Or in the browser:
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```html
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<script src="dist/ba-foreach.min.js"></script>
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<script>
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forEach(["a", "b", "c"], function(item, index, arr) {
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console.log("each", item, index, arr);
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});
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// logs:
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// each a 0 ["a", "b", "c"]
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// each b 1 ["a", "b", "c"]
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// each c 2 ["a", "b", "c"]
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</script>
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```
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In the browser, you can attach the forEach method to any object.
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```html
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<script>
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this.exports = Bocoup.utils;
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</script>
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<script src="dist/ba-foreach.min.js"></script>
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<script>
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Bocoup.utils.forEach(["a", "b", "c"], function(item, index, arr) {
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console.log("each", item, index, arr);
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});
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// logs:
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// each a 0 ["a", "b", "c"]
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// each b 1 ["a", "b", "c"]
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// each c 2 ["a", "b", "c"]
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</script>
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```
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## The General Idea (Why I thought this was worth sharing)
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The idea is to allow the callback to decide _at runtime_ whether the loop will be synchronous or asynchronous. By using `this` in a creative way (in situations where that value isn't already spoken for), an entire control API can be offered without over-complicating function signatures.
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```javascript
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forEach(arr, function(item, index) {
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// Synchronous.
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});
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forEach(arr, function(item, index) {
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// Only when `this.async` is called does iteration becomes asynchronous. The
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// loop won't be continued until the `done` function is executed.
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var done = this.async();
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// Continue in one second.
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setTimeout(done, 1000);
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});
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forEach(arr, function(item, index) {
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// Break out of synchronous iteration early by returning false.
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return index !== 1;
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});
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forEach(arr, function(item, index) {
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// Break out of asynchronous iteration early...
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var done = this.async();
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// ...by passing false to the done function.
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setTimeout(function() {
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done(index !== 1);
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});
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});
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```
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## Examples
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See the unit tests for more examples.
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```javascript
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// Generic "done" callback.
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function allDone(notAborted, arr) {
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console.log("done", notAborted, arr);
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}
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// Synchronous.
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forEach(["a", "b", "c"], function(item, index, arr) {
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console.log("each", item, index, arr);
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}, allDone);
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// logs:
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// each a 0 ["a", "b", "c"]
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// each b 1 ["a", "b", "c"]
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// each c 2 ["a", "b", "c"]
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// done true ["a", "b", "c"]
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// Synchronous with early abort.
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forEach(["a", "b", "c"], function(item, index, arr) {
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console.log("each", item, index, arr);
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if (item === "b") { return false; }
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}, allDone);
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// logs:
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// each a 0 ["a", "b", "c"]
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// each b 1 ["a", "b", "c"]
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// done false ["a", "b", "c"]
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// Asynchronous.
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forEach(["a", "b", "c"], function(item, index, arr) {
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console.log("each", item, index, arr);
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var done = this.async();
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setTimeout(function() {
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done();
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}, 500);
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}, allDone);
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// logs:
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// each a 0 ["a", "b", "c"]
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// each b 1 ["a", "b", "c"]
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// each c 2 ["a", "b", "c"]
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// done true ["a", "b", "c"]
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// Asynchronous with early abort.
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forEach(["a", "b", "c"], function(item, index, arr) {
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console.log("each", item, index, arr);
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var done = this.async();
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setTimeout(function() {
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done(item !== "b");
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}, 500);
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}, allDone);
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// logs:
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// each a 0 ["a", "b", "c"]
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// each b 1 ["a", "b", "c"]
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// done false ["a", "b", "c"]
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// Not actually asynchronous.
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forEach(["a", "b", "c"], function(item, index, arr) {
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console.log("each", item, index, arr);
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var done = this.async()
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done();
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}, allDone);
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// logs:
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// each a 0 ["a", "b", "c"]
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// each b 1 ["a", "b", "c"]
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// each c 2 ["a", "b", "c"]
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// done true ["a", "b", "c"]
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// Not actually asynchronous with early abort.
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forEach(["a", "b", "c"], function(item, index, arr) {
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console.log("each", item, index, arr);
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var done = this.async();
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done(item !== "b");
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}, allDone);
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// logs:
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// each a 0 ["a", "b", "c"]
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// each b 1 ["a", "b", "c"]
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// done false ["a", "b", "c"]
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```
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## Contributing
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In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint and test your code using [grunt](https://github.com/cowboy/grunt).
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_Also, please don't edit files in the "dist" subdirectory as they are generated via grunt. You'll find source code in the "lib" subdirectory!_
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## Release History
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04/29/2013
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v0.1.3
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Removed hard Node.js version dependency.
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11/17/2011
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v0.1.2
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Adding sparse array support.
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Invalid length properties are now sanitized.
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This closes issue #1 (like a boss).
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11/11/2011
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v0.1.1
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Refactored code to be much simpler. Yay for unit tests!
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11/11/2011
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v0.1.0
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Initial Release.
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## License
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Copyright (c) 2012 "Cowboy" Ben Alman
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Licensed under the MIT license.
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<http://benalman.com/about/license/>
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