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92 lines
1.8 KiB
Markdown
92 lines
1.8 KiB
Markdown
---
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date: 2020-11-13
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id: 1e9f826e-69c6-4a52-8cf8-135abc082fb3
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title: JavaScript Symbols
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---
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- [JavaScript Symbol Prototype
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Methods](20201116101443-javascript_symbol_prototype_methods)
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# Description
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These are tokens that serve as unique IDs. You create symbols via the
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factory function `Symbol()` (which is loosely similar to
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[string](20200922164551-strings) returning strings if called as a
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function).
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# Syntax
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``` javascript
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const symbol1 = Symbol();
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```
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## Add a description
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``` javascript
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const tralala = Symbol('tralala')
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console.log(tralala) // Symbol(tralala)
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```
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## Convert to string
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``` javascript
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const tralala = Symbol('tralala')
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console.log(String(tralala)) // `Symbol(tralala)`
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```
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## Every Symbol is unique
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``` javascript
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console.log(Symbol() === Symbol()) // false
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```
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## Property keys
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``` javascript
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const KEY = Symbol();
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const obj = {};
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obj[KEY] = 123;
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console.log(obj[KEY]); // 123
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```
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``` javascript
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const FOO = Symbol();
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const obj = {
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[FOO]() {
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return 'bar';
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}
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};
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console.log(obj[FOO]()); // bar
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```
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# Use as reserved inherited method names
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If for some bizarre reason you want to use reserved inherited method
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names yourself (like toString) you can with Symbols.
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``` javascript
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const toStringSymbol = Symbol("toString");
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Array.prototype[toStringSymbol] = function() {
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return `${this.length} cm of blue yarn`;
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};
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console.log([1, 2].toString()); //1, 2
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console.log([1, 2][toStringSymbol]()); // 2 cm of blue yarn
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```
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# Expressions
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Symbols can also be used in [object](20200826201605-objects) expressions
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and [classes](20201008090316-class_notation).
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``` javascript
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const toStringSymbol = Symbol("toString");
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let stringObject = {
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[toStringSymbol]() {
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return "a jute rope";
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},
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};
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console.log(stringObject[toStringSymbol]()); // a jute rope
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```
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