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[JS] Fix typo (#161)

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Eunice Park 2019-01-15 01:44:28 -08:00 committed by Yangshun Tay
parent 6a026fdcdb
commit a17caf8011
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@ -830,7 +830,7 @@ Practically, ES2015 has vastly improved JavaScript and made it much nicer to wri
For objects:
* `for` loops - `for (var property in obj) { console.log(property); }`. However, this will also iterate through its inherited properties, and you will add an `obj.hasOwnProperty(property)` check before using it.
* `for-in` loops - `for (var property in obj) { console.log(property); }`. However, this will also iterate through its inherited properties, and you will add an `obj.hasOwnProperty(property)` check before using it.
* `Object.keys()` - `Object.keys(obj).forEach(function (property) { ... })`. `Object.keys()` is a static method that will lists all enumerable properties of the object that you pass it.
* `Object.getOwnPropertyNames()` - `Object.getOwnPropertyNames(obj).forEach(function (property) { ... })`. `Object.getOwnPropertyNames()` is a static method that will lists all enumerable and non-enumerable properties of the object that you pass it.
@ -838,7 +838,7 @@ For arrays:
* `for` loops - `for (var i = 0; i < arr.length; i++)`. The common pitfall here is that `var` is in the function scope and not the block scope and most of the time you would want block scoped iterator variable. ES2015 introduces `let` which has block scope and it is recommended to use that instead. So this becomes: `for (let i = 0; i < arr.length; i++)`.
* `forEach` - `arr.forEach(function (el, index) { ... })`. This construct can be more convenient at times because you do not have to use the `index` if all you need is the array elements. There are also the `every` and `some` methods which will allow you to terminate the iteration early.
* `for-of` loops - `for (let elem of arr) { ... }`. ES6 introduces a new loop, the `for-of` loop, that allows you to loop over objects that conform to the [iterable protocol](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) such as `String`, `Array`, `Map`, `Set`, etc. It combines the advantages of the `for` loop and the `forEach()` method. The advantage of the `for-of` loop is that you can break from it, and the advantage of `forEach()` is that it is more concise than the `for` loop because you don't need a counter variable. With the `for-of` loop, you get both the ability to break from a loop and a more concise syntax.
* `for-of` loops - `for (let elem of arr) { ... }`. ES6 introduces a new loop, the `for-of` loop, that allows you to loop over objects that conform to the [iterable protocol](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterable_protocol) such as `String`, `Array`, `Map`, `Set`, etc. It combines the advantages of the `for` loop and the `forEach()` method. The advantage of the `for` loop is that you can break from it, and the advantage of `forEach()` is that it is more concise than the `for` loop because you don't need a counter variable. With the `for-of` loop, you get both the ability to break from a loop and a more concise syntax.
Most of the time, I would prefer the `.forEach` method, but it really depends on what you are trying to do. Before ES6, we used `for` loops when we needed to prematurely terminate the loop using `break`. But now with ES6, we can do that with `for-of` loops. I would use `for` loops when I need even more flexibility, such as incrementing the iterator more than once per loop.