Symbol Detailed Explanation and Usage

Foreword:

The attribute names of objects in ES5 are all strings, which is easy to cause duplicate names and pollute the environment

1. What is Symbol?

Symbol is a new basic data type introduced in ES6, which is used to represent a unique value. It is the seventh data type in JavaScript, alongside undefined, null, Number (value), String (string), Boolean (Boolean), and Object (object).

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Second, the characteristics of Symbol

1. The value corresponding to the Symbol attribute is unique, which solves the problem of naming conflicts

let symbol = Symbol("one")
let symbol1 = Symbol("one")
console.log(symbol)
// 结果：Symbol("one")

2. Symbol values ​​cannot be calculated with other data, including matching strings

let a = Symbol()
let b = a+1
console.log(b)
// 结果：报错

3. For in, for of does not traverse symbol attributes when traversing.

let symbol = Symbol();
let obj = {};
obj[symbol] = 'hello';

for(var i in obj){
	console.log(obj[i])
}
// 结果：报错

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3. The use of Symbol

1. Call the Symbol function to get the symbol value

let symbol = Symbol();
let obj = {};
obj[symbol] = 'hello';

for(var i in obj){
	console.log(obj[i])
}
// 结果：报错

2. Parameter ID

let symbol = Symbol('one');
let symbol2 = Symbol('two');
console.log(symbol);// Symbol('one')
console.log(symbol2);// Symbol('two')

3. Built-in Symbol value

• In addition to defining the Symbol value used by itself, ES6 also provides 11 built-in Symbol values, which point to the methods used internally by the language.
  • Symbol.iterator
• The Symbol.iterator property of the object points to the object's default traverser method (described later)

4. symbol != symbol symbol is unique

let one = Symbol("one")
let two = Symbol("one")

console.log(one == two)
// 结果：false

5. Create the attribute value of symbol

let symbol = Symbol()
   
let obj = {name:"张三疯",age:18}

6. fon in for of will not traverse symbols

obj[symbol] = "123"
console.log(obj)
for(var v in obj){
   console.log(obj[v])
}
// 结果：报错

7. Symbol values ​​cannot be operated on with values ​​of other types

let obj = {
	toString(){
		return "123"
	}
}
let a = Symbol(obj)
console.log(a+'1234')
// 结果：报错

8. Symbol values ​​can be explicitly converted to strings.

let obj = {
	toString(){
		return "123"
	}
}
let a = Symbol(obj)

console.log(String(a))
// Symbol(123)
console.log(a == String(a))
// false

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Summarize:

That's allDetailed explanation and usage of the new Symbol in ES6If you don’t understand, you can ask me in the comment area or chat with me privately. I will continue to release some new functions in the future, so stay tuned.
My other articles: https://blog.csdn.net/weixin_62897746?type=blog