实现call apply 手写call apply

/ call模拟
Function.prototype.call_ = function (obj) {
    //判断是否为null或者undefined,同时考虑传递参数不是对象情况
    obj = obj ? Object(obj) : window;
    var args = [];
    // 注意i从1开始
    for (var i = 1, len = arguments.length; i < len; i++) {
        args.push("arguments[" + i + "]");
    };
    obj.fn = this; // 此时this就是函数fn
    var result = eval("obj.fn(" + args + ")"); // 执行fn
    delete obj.fn; //删除fn
    return result;
};
// apply模拟
Function.prototype.apply_ = function (obj, arr) {
    obj = obj ? Object(obj) : window;
    obj.fn = this;
    var result;
    if (!arr) {
        result = obj.fn();
    } else {
        var args = [];
        // 注意这里的i从0开始
        for (var i = 0, len = arr.length; i < len; i++) {
            args.push("arr[" + i + "]");
        };
        result = eval("obj.fn(" + args + ")"); // 执行fn
    };
    delete obj.fn; //删除fn
    return result;
};

// 第二种写法  
// ES6 call
Function.prototype.call_ = function (obj) {
    obj = obj ? Object(obj) : window;
    obj.fn = this;
    // 利用拓展运算符直接将arguments转为数组
    let args = [...arguments].slice(1);
    let result = obj.fn(...args);

    delete obj.fn
    return result;
};
// ES6 apply
Function.prototype.apply_ = function (obj, arr) {
    obj = obj ? Object(obj) : window;
    obj.fn = this;
    let result;
    if (!arr) {
        result = obj.fn();
    } else {
        result = obj.fn(...arr);
    };

    delete obj.fn
    return result;
};

转自： https://www.cnblogs.com/echolun/p/12144344.html