JavaScript 问题 - 有没有办法在不使用调用、应用和绑定方法的情况下将对象分配给"this"关键字？

Question

我正在尝试为调用、应用和绑定方法创建一个polyfill。

const user = {
firstName: "Christopher",
lastName: "Nolan",
};
const fullName = function (place, country) {
console.log(
`${this.firstName} ${this.lastName} is from ${place}, ${country}.`
);
};

//使用调用方法

fullName.call(user, "London", "UK");

//重新创建一个名为"的调用方法_呼叫"；

Function.prototype._call = function (...args) {
const funcObj = this;
const params = args.slice(1);
return (function () {
const obj = args[0];

// How can I point out the obj to "this" keyword inside a funcObj without using the bind method as I mentioned below.
return funcObj.bind(obj, ...params)();
})();
};
fullName._call(user, "London", "UK");

Answer 1

是。只需使用

var myObject = this;

我理解你可能遇到的问题。有时，当您希望使用"this"对象时，"this"的上下文已经更改。有些人使用

var that = this;

以下是一些更深入的阅读内容。

https://dbwriteups.wordpress.com/2017/04/08/what-does-that-this-in-javascript-mean/

Answer 2

我不确定这是一个很好的实现，但您可以利用这样一个事实，即对于对象方法，作用域会自动设置为调用它的对象。

考虑到这一点，您可以使用范围作为原型创建一个对象，并将原始函数添加为方法，然后调用该方法。

const user = {
firstName: "Christopher",
lastName: "Nolan",
};
const fullName = function (place, country) {
console.log(
`${this.firstName} ${this.lastName} is from ${place}, ${country}.`
);
};
Function.prototype._call = function (scope, ...args) {
// symbol for the method name to avoid name collisions
const symbol = Symbol();

// create a new object from scope with the original function (this) as a method
const temp = Object.create(scope, {[symbol]: { value: this }});

// inside the method "this" will point to "temp" which is (effectively) "scope"
return temp[symbol](...args);
}
fullName._call(user, 'London', 'UK');