手写实现call、apply和bind是面试中常考的手写题，这里提供几个手写方案。

call

Function.prototype.myCall(thisArg, ...args){
    //1. 获取调用call的函数对象
    let fn = this
    //2. 获取要绑定的对象
    thisArg = thisArg !== null && thisArg !== undefined ? Object(thisArg) : window
    //3. 将绑定的对象上加上fn
    thisArg.fn = fn
    //4. 执行并获取结果
    return thisArg.fn(...args)
}

apply

Function.prototype.myApply(thisArg, argArray){
    let fn = this
    thisArg = thisArg !== null && thisArg !== undefined ? Object(thisArg) : window
    thisArg.fn = fn
    return thisArg.fn(...(argArray || [])) //如果没有值的话赋值空数组，否则用不了。
}

bind

Function.prototype.myBind(thisArg, ...args1){
    let fn = this
    function proxyFn(...args2){
        thisArg = thisArg !== null && thisArg !== undefined ? Object(thisArg) : window
        thisArg.fn = fn
        let result = thisArg.fn(...[...args1,...args2])
        delete thisArg.fn
        return result
    }
    return proxyFn
}