Detailed explanation of the usage of ES6 Symbol (with code)

This article brings you a detailed explanation of the usage of ES6 Symbol (with code). It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

1. Symbol is a new data type in ES6, which provides unique values ​​

{
    // 声明，Symbol声明的变量是唯一的
    let a1 = Symbol();
    let a2 = Symbol();
    console.log(a1 === a2); // false
    // Symbol.for()接收一个参数，作为key值
    // 使用for方法时，会检查这个key值在全局是否注册
    // 如果注册过就返回这个值，否则调用Symbol生成新的独一无二的值
    let a3 = Symbol.for('a3');
    let a4 = Symbol.for('a3');
    console.log(a3 === a4); // true
}

2. Declare Symbol type attributes in the object

{
    let a1 = Symbol.for('abc');
    let obj = {
        [a1]: '123',
        'abc': '345',
        'df': '456',
    };
    console.log(obj); // {abc: "345", df: "456", Symbol(abc): "123"}
}

3.Symbol Traverse

{
    let a1 = Symbol.for('abc');
    let obj = {
        [a1]: '123',
        'abc': 345,
        'df': 456,
    };
    // let of（或者for in）循环拿不到 以Symbol作为属性的值
    for (let key of Object.keys(obj)) {
        console.log(key); // abc  df
    }

    // 只拿到以Symbol作为属性的值，getOwnPropertySymbols返回一个数组
    Object.getOwnPropertySymbols(obj).forEach(function (item) {
        console.log(obj[item]); // 123
    });

    // 对象全部属性和值都拿到，包括Symbol。Reflect.ownKeys返回一个数组
    Reflect.ownKeys(obj).forEach(function (item) {
        console.log(item, obj[item]); // abc 345  df 456  Symbol(abc) "123"
    });
}

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