1. call

javascript">Function.prototype.myCall = function (context) {
	// context 接收第一个参数 如果没有默认用window
	context = context || window
	// 给context.fn 或其他属性赋值为函数, 即myCall的调用者改变函数的this 指向context
	context.fn = this
	// 获取传入的参数
	const args = [...arguments].slice(1)
	// 通过...展开并传给fn args 获取执行结果 result 并返回
	const result = context.fn(...args)
	// 删除fn
	delete context.fn
	return result
}

2. apply

javascript">Function.prototype.myApply = function (context) {
	context = context || window
	context.fn = this
	let result
	if (arguments[1]) {
		result = context.fn(...arguments[1])
	} else {
		result = context.fn()
	}
	delete context.fn
	return result
}

3. bind

javascript">Function.prototype.myBind = function (context) {
	context = context || window
	const args = [...arguments].slice(1)
	let _this = this
	return function f () {
		return _this.apply(context, [...args, ...arguments])
	}
}