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js函数式编程
本文是看完冴羽大大的博客后的笔记
使用一个指定的this值和若干个指定参数的情况下调用某个函数和某个方法
call的实现:改变this指向,指向绑定的对象,执行函数
`Function.prototype.call2 = function (context) {
context = context || window;
//this:绑定的函数
context.fn = this;
var args = [];
for (var i = 1; i < arguments.length; i++) {
//从1开始,也就是从要绑定的对象之后开始视作传入参数
args.push('arguments[' + i + ']');
}
var result = eval('context.fn(' + args + ')');
//为对象创建了一个方法,为方法传入参数执行完毕后,删除这个方法
delete context.fn;
return result;
};
var foo = {
a: 2
};
var bar = function () {
console.log(this.a);
};
bar.call2(foo);
//apply的实现,跟call的区别之处,传入参数为数组形式
Function.prototype.apply2 = function (context, arr) {
context = Object(context) || window;
context.fn = this;
var result;
//传入的不是对象,视作无对象直接执行函数
if (!arr) {
result = context.fn();
} else {
var args = [];
for (var i = 1, len = arguments.length; i < len; i++) {
args.push('arguments[' + i + ']');
}
result = eval('context.fn(' + args + ')');
}
delete context.fn;
return result;
};
Function.prototype.bind2 = function (context) {
if (typeof this !== "function") {
throw new Error("Function.prototype.bind - what is trying to be bound is not callable");
}
var self = this;
var args = [].slice.call(arguments, 1);
//中间对象fNop,这样继承构造函数的对象修改它的原型不会把self的原型一起修改
var fNop = function () { };
var fBound = function () {
var bindArgs = [].slice.call(arguments);
//若将返回的函数作为构造函数新建一个实例,则将this绑定到这个新建的对象上。如果作为普通函数,则正常传参
return self.apply(this instanceof fBound ? this : context, args.concat(bindArgs));
};
fNop.prototype = self.prototype;
fBound.prototype = new fNop();
return fBound;
};
function objectFactory() {
var obj = new Object(),
constructor = [].shift.call(arguments);
//指向构造函数的原型
obj.proto = constructor.prototype;
//将构造函数的this指向新建对象,这样对象可以访问构造函数上的属性
var ret = constructor.apply(obj, arguments);
//如果构造返回值是一个对象,则返回这个对象,如果不是对象,改返回什么就返回什么
return typeof ret === 'object' ? ret : obj;
}`
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