ES6数组判断以及原始值转换

一. 数组判断

1. 情况一

const target = {}

function isArray(target) {
    return Object.prototype.toString.call(target) === "[object Array]"
}
console.log(isArray(target)) // false

const target = {
    [Symbol.toStringTag]: "Array",
}

function isArray(target) {
    return Object.prototype.toString.call(target) === "[object Array]"
}
console.log(isArray(target)) // true

2. 情况二

const target = {}

function isArray(target) {
    return target instanceof Array
}

console.log(isArray(target)) // false

const target = {}
Object.setPrototypeOf(target, Array.prototype)
function isArray(target) {
    return target instanceof Array
}

console.log(isArray(target)) // true

使用ES6

const target = {
    [Symbol.toStringTag]: "Array",
}

Object.setPrototypeOf(target, Array.prototype)

function isArray(target) {
    return Array.isArray(target)
}

console.log(isArray(target)) // false

二. 原始值转换

1. 情况一

const target = {}
console.log(target.toString()) // [object Object]
console.log(target + 1) // [object Object]1

2. 情况二

const target = {
    toString() { return 1 },
}
console.log(target.toString()) // 1
console.log(target + 1) // 2

3. 情况三

const target = {
    toString() { return 1 },
    valueOf() {
        return 2
    },
}
console.log(target.toString()) // 1
console.log(target + 1) // 3

4. 情况四 参考mdn

const target = {
    toString() { return 1 },
    valueOf() {
        return 2
    },
    [Symbol.toPrimitive](hint) {
        return 3
    },
}
console.log(target.toString()) // 1
console.log(target + 1) // 4

原始值强制转换优先权重:[Symbol.toPrimitive] > valueOf > toString