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108 lines
2.2 KiB
Markdown
108 lines
2.2 KiB
Markdown
---
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date: 2020-10-09
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id: c76b3766-a1ed-43f9-bdb6-4076e6bb5b7a
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title: JavaScript Array Methods
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---
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# ES6
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## Static Array methods
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### Array.from()
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``` javascript
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const arr2 = Array.from(arguments); // ES6
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```
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If a value is [iterable](20201014092625-javascript_iterables) (as all
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Array-like DOM data structure are by now), you can also use the
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[spread](20201014094144-spread) operator (…) to convert it to an
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[Array](20200826201029-arrays):
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``` javascript
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const arr1 = [...'abc'];
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// ['a', 'b', 'c']
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const arr2 = [...new Set().add('a').add('b')];
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// ['a', 'b']
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```
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### Array.of()
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This returns an array of the passed parameters
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``` javascript
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console.log(Array.of(1, 2, 3, 4)) // [1, 2, 3, 4]
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```
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## Array.prototype methods
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### Array.prototype.fill()
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``` javascript
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const arr2 = new Array(2).fill(undefined);
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// [undefined, undefined]
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```
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### Array.prototype.copyWithin()
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The method signature is:
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``` typescript
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Array.prototype.copyWithin(target : number,
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start : number, end = this.length) : This
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```
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It copies the elements whose indices are in the range \[start,end) to
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index target and subsequent indices. If the two index ranges overlap,
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care is taken that all source elements are copied before they are
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overwritten. I am confused as to how this is in any way useful.
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``` javascript
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const arr = [0,1,2,3];
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console.log(arr.copyWithin(2, 0, 2)) // [0, 1, 0, 1]
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```
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### Searching for elements
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1. Array.prototype.findIndex()
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``` javascript
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console.log([6, -6, 8].findIndex(x => x < 0)) // 1
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```
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2. Array.prototype.find()
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``` javascript
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console.log([6, -6, 8].find(x => x < 0)) // -6
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```
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### Iteration
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1. Array.prototype.entries()
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``` javascript
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console.log(Array.from(['a', 'b'].entries())) // [ [ 0, 'a' ], [ 1, 'b' ] ]
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```
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2. Array.prototype.values()
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``` javascript
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console.log(Array.from(['a', 'b'].values())) // ['a', 'b']
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```
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3. Array.prototype.keys()
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``` javascript
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console.log(Array.from(['a', 'b'].keys())) // [0, 1]
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```
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# ES2016
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## Array.prototype.includes()
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Tells you if array includes a certain element:
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``` javascript
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console.log(["a", "b", "c"].includes("a")); // true
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console.log(["a", "b", "c"].includes("d")); // false
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```
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