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30secondsofcode
2020-01-20 08:13:33 +00:00
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blog_data/snippetList.json
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@ -30,6 +30,23 @@
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}
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"id": "javascript-for-in-for-of-foreach",
"type": "snippetListing",
"title": "What is the difference between JavaScript's for...in, for...of and forEach?",
"attributes": {
"text": "`for...in` is used to iterate over all enumerable properties of an object, including inherited enumerable properties. \nThis iteration statement can be used with arrays strings or plain objects, but not with `Map` or `Set` objects.\n\n```js\nfor (let prop in ['a', 'b', 'c']) \n console.log(prop); // 0, 1, 2 (array indexes)\n\nfor (let prop in 'str') \n console.log(prop); // 0, 1, 2 (string indexes)\n\nfor (let prop in {a: 1, b: 2, c: 3}) \n console.log(prop); // a, b, c (object property names)\n\nfor (let prop in new Set(['a', 'b', 'a', 'd'])) \n console.log(prop); // undefined (no enumerable properties)\n```\n\n`for...of` is used to iterate over iterable objects, iterating over their values instead of their properties.\nThis iteration statement can be used with arrays, strings, `Map` or `Set` objects, but not with plain objects.\n\n```js\nfor (let val of ['a', 'b', 'c']) \n console.log(val); // a, b, c (array values)\n\nfor (let val of 'str') \n console.log(val); // s, t, r (string characters)\n\nfor (let val of {a: 1, b: 2, c: 3}) \n console.log(prop); // TypeError (not iterable)\n\nfor (let val of new Set(['a', 'b', 'a', 'd'])) \n console.log(val); // a, b, d (Set values)\n```\n\nFinally, `forEach()` is a method of the `Array` prototype, which allowes you to iterate over the elements of an array.\nWhile `forEach()` only iterates over arrays, it can access both the value and the index of each element while iterating.\n\n```js\n['a', 'b', 'c'].forEach(\n val => console.log(val) // a, b, c (array values)\n);\n\n['a', 'b', 'c'].forEach(\n (val, i) => console.log(i) // 0, 1, 2 (array indexes)\n);\n```\n\n**Image credit:** [Tim Stief](https://unsplash.com/@timstief?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText) on [Unsplash](https://unsplash.com/s/photos/code?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText)\n",
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blog_data/snippets.json
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@ -50,6 +50,32 @@
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"id": "javascript-for-in-for-of-foreach",
"title": "What is the difference between JavaScript's for...in, for...of and forEach?",
"type": "blog.question",
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"fileName": "javascript-for-in-for-of-foreach.md",
"cover": "blog_images/javascript-for-in-for-of-foreach.jpg",
"authors": [
"chalarangelo"
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"text": "`for...in` is used to iterate over all enumerable properties of an object, including inherited enumerable properties. \nThis iteration statement can be used with arrays strings or plain objects, but not with `Map` or `Set` objects.\n\n```js\nfor (let prop in ['a', 'b', 'c']) \n console.log(prop); // 0, 1, 2 (array indexes)\n\nfor (let prop in 'str') \n console.log(prop); // 0, 1, 2 (string indexes)\n\nfor (let prop in {a: 1, b: 2, c: 3}) \n console.log(prop); // a, b, c (object property names)\n\nfor (let prop in new Set(['a', 'b', 'a', 'd'])) \n console.log(prop); // undefined (no enumerable properties)\n```\n\n`for...of` is used to iterate over iterable objects, iterating over their values instead of their properties.\nThis iteration statement can be used with arrays, strings, `Map` or `Set` objects, but not with plain objects.\n\n```js\nfor (let val of ['a', 'b', 'c']) \n console.log(val); // a, b, c (array values)\n\nfor (let val of 'str') \n console.log(val); // s, t, r (string characters)\n\nfor (let val of {a: 1, b: 2, c: 3}) \n console.log(prop); // TypeError (not iterable)\n\nfor (let val of new Set(['a', 'b', 'a', 'd'])) \n console.log(val); // a, b, d (Set values)\n```\n\nFinally, `forEach()` is a method of the `Array` prototype, which allowes you to iterate over the elements of an array.\nWhile `forEach()` only iterates over arrays, it can access both the value and the index of each element while iterating.\n\n```js\n['a', 'b', 'c'].forEach(\n val => console.log(val) // a, b, c (array values)\n);\n\n['a', 'b', 'c'].forEach(\n (val, i) => console.log(i) // 0, 1, 2 (array indexes)\n);\n```\n\n**Image credit:** [Tim Stief](https://unsplash.com/@timstief?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText) on [Unsplash](https://unsplash.com/s/photos/code?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText)\n",
"tags": [
"javascript",
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"id": "testing-stateful-ui-components",
"title": "An approach to testing stateful React components",