ES6 new symbol data type

1.Symbol Is a new data type , It means a unique ( Any two Symbol Types are not equal ),

Symbol Type is also a kind of basic type , adopt Symbol Function to get

const sym1 = Symbol()

const sym2 = Symbol()

console.log(sym1)

console.log(typeof sym1)

console.log(stm1 === sym2)

 2.Symbol Function can take a string as an argument , Said to the Symbol Description of the example , Easy to distinguish

const sym3 = Symbol("name")

const sym4 = Symbol("address")

console.log(sym3)

console.log(sym4)

console.log(sym3 === sym4)

const sym3 = Symbol("name")

const sym4 = Symbol("name")

console.log(sym3)

console.log(sym4)

console.log(sym3 === sym4)

Symbol Equal or not Symbol() It doesn't matter to describe the information inside

3. If the description information is the same , Want to get two of the same Symbol() value , have access to Symbol.for()

const sym5 = Symbol.for("name")

const sym6 = Symbol.for("name")

console.log(sym5)

console.log(sym5 === sym6)

 

 4. purpose : As an attribute of an object , The advantage is that attributes do not override ( Each from Symbol() Back to symbol Value is the only ,symbol As the identifier of the object property , This is the only purpose of this data type )

Be careful :

• Symbol Value as object property name , You can't use the dot operator .
• Symbol As property name , When traversing objects , This attribute will not appear in for .. in In circulation , And not by Object.keys() / Object.getOwnPropertyNames() / JSON.stringify() return
• adopt Object.getOwnPropertySymbol() Method , You can get all of the Symbol Property name

Object.getOwnPropertySymbol() It is used to get all of the specified objects Symbol Attribute name

 const key1 = Symbol("tiger")

 const key2 = Symbol("flag")

const o = {

a:1,   b:2,

[key1]: 2022, [key2]:" A rich man "  }

console.log(o[key1],o[key2])

// When variables are used as attributes of objects , Add variables as attributes through square brackets

Equivalent to :  o[key1] = 2022 o[key2] = " A rich man "

console.log(Object.key(o) )

console.log(Object.getOwnPropertySymbols(0))