Function.prototype.call2 = function (context) {
var context = context || window;
context.fn = this;
var args = [];
for(var i = 1, len = arguments.length; i < len; i++) {
args.push('arguments[' + i + ']');
}
var result = eval('context.fn(' + args +')');
delete context.fn
return result;
}
Function.prototype.call3 = function (context) {
let context = context || window;
context.fn = this;
let args = [...arguments].slice(1)
let result = context.fn(...args)
delete context.fn
return result;
}
Function.prototype.myApply = function (context) {
if (typeof this !== 'function') {
throw new TypeError('Error')
}
if (context === null || context === undefined) {
context = window // 指定为 null 和 undefined 的 this 值会自动指向全局对象(浏览器中为window)
} else {
context = Object(context) // 值为原始值（数字，字符串，布尔值）的 this 会指向该原始值的实例对象
}
context.fn = this
let result
//判断是否存在第二个参数
//如果存在就将第二个参数也展开
if(arguments[1]) {
result = context.fn(...arguments[1])
} else {
result = context.fn()
}
delete context.fn
return result
}
// 测试一下
var value = 2;
var obj = {
value: 1
}
function bar(name, age) {
console.log(this.value);
return {
value: this.value,
name: name,
age: age
}
}
bar.call(null); // 2
console.log(bar.call3(obj, 'Cherry', 18));
console.log(bar.myApply(obj, ['Cherry', 18]));