JS Symbol

Symbol

Symbol.species

用于控制生成新实例时，类的内置方法使用哪个构造器

Symbol.iterator

用于生成对象的迭代器

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var a = {
    1: "张三",
    2: "12"
}
a[Symbol.iterator] = function() {
    index = 0;
    return {
        next: ()=>{
            index++;
            return {
                value: this[index],
                done: !this[index]
            }
        }

    }
}

for (var i of a) {
    console.log(i)
    //张三
    //12
}

Symbol.toPrimitive

在做类型转换时，将对象转为原生类型值

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var arr = [1, 2, 3, 4]

console.log(arr + 10)
// 1,2,3,410

arr[Symbol.toPrimitive] = function(hint) {
    if (hint === "default" || hint === "number") {
        return this.reduce((acc,curr)=>acc + curr, 0)
    }
}
console.log(arr + 10)
//20

Symbool