Symbol Overview | 點燈坊

Symbol is a new type for unique value in ECMAScript 2015.

Version

ECMAScript 2015

let s = Symbol () // ?
typeof s // ?

Symbol can be created by Symbol, and its type is symbol.

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let s = new Symbol () // ?

Symbol can’t be created by new, since Symbol is not a constructor function.

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let s = Symbol () // ?
s.toString () // ?
console.log (s)

Symbol provides toString to transform Symbol into String; its value is Symbol()
If we use console.log to show Symbol, it will use toString to transform into String first and then show the result

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let s1 = Symbol ()
let s2 = Symbol ()

s1 === s2 // ?

Symbol always returns unique value.

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let s1 = Symbol ('Sam')
let s2 = Symbol ('Sam')

s1 === s2 // ?

We can provide String to Symbol, but it’s just for description. Symbol still returns a unique value.

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let s1 = Symbol.for ('Sam')
let s2 = Symbol.for ('Sam')

s1 === s2 // ?

If we want same description represents the same value, we can Symbol.for instead of Symbol.

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