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97 lines
1.5 KiB
Markdown
97 lines
1.5 KiB
Markdown
---
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date: 2020-10-12
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id: 0ad60ce3-4e34-490e-a565-a0ce330e6fc8
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title: JavaScript Maps
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---
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# Description
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For sane people [ES6](20201030093404-es6) comes with a <s>half assed
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"solution"</s> handy data structure called `Map` which prevents the diy
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shenanigans below.
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# Syntax
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## Basic operation
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### Single entries
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``` javascript
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const map = new Map();
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const KEY = {};
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map.set(KEY, 123);
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console.log(map.get(KEY)); // 123
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console.log(map.has(KEY)); // true
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map.delete(KEY);
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console.log(map.has(KEY)); // false
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```
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### Array
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``` javascript
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const map = new Map([
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[ 1, 'one' ],
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[ 2, 'two' ],
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[ 3, 'three' ],
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]);
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```
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## Iteration
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### Keys
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``` javascript
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const map = new Map([
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[false, 'no'],
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[true, 'yes'],
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]);
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for (const key of map.keys()) {
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console.log(key);
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}
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```
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### Values
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``` javascript
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const map = new Map([
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[false, 'no'],
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[true, 'yes'],
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]);
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for (const value of map.values()) {
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console.log(value);
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}
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```
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### Entries
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``` javascript
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const map = new Map([
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[false, "no"],
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[true, "yes"],
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]);
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for (const entry of map.entries()) {
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console.log(entry[0], entry[1]);
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}
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```
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### Converting to Arrays
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The [spread](20201014094144-spread) operator (…) can turn an
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[iterable](20201014092625-javascript_iterables) into an
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[Array](20200826201029-arrays)
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``` javascript
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const map = new Map().set(false, 'no').set(true, 'yes');
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console.log([...map.keys()]) // false, true
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```
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``` javascript
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const map = new Map().set(false, 'no').set(true, 'yes');
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console.log([...map])
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```
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