我已经知道apply和call是类似的函数,它们设置this(函数的上下文)。
区别在于我们发送参数的方式(manual vs array)
问题:
但是什么时候应该使用bind()方法呢?
var obj = {
x: 81,
getX: function() {
return this.x;
}
};
alert(obj.getX.bind(obj)());
alert(obj.getX.call(obj));
alert(obj.getX.apply(obj));
jsbin
语法
呼叫(thisArg, arg1, arg2, .)
(thisArg专心,argsArray)
bind(thisArg[, arg1] [, arg2])
Here
thisArg是对象
argArray是一个数组对象
Arg1, arg2, arg3,…是额外的参数
function printBye(message1, message2){
console.log(message1 + " " + this.name + " "+ message2);
}
var par01 = { name:"John" };
var msgArray = ["Bye", "Never come again..."];
printBye.call(par01, "Bye", "Never come again...");
//Bye John Never come again...
printBye.call(par01, msgArray);
//Bye,Never come again... John undefined
//so call() doesn't work with array and better with comma seperated parameters
//printBye.apply(par01, "Bye", "Never come again...");//Error
printBye.apply(par01, msgArray);
//Bye John Never come again...
var func1 = printBye.bind(par01, "Bye", "Never come again...");
func1();//Bye John Never come again...
var func2 = printBye.bind(par01, msgArray);
func2();//Bye,Never come again... John undefined
//so bind() doesn't work with array and better with comma seperated parameters
调用/apply立即执行函数:
func.call(context, arguments);
func.apply(context, [argument1,argument2,..]);
Bind不会立即执行函数,而是返回包装好的apply函数(供以后执行):
function bind(func, context) {
return function() {
return func.apply(context, arguments);
};
}
它们都将其附加到函数(或对象)中,区别在于函数调用(见下文)。
Call将此附加到函数中并立即执行函数:
var person = {
name: "James Smith",
hello: function(thing) {
console.log(this.name + " says hello " + thing);
}
}
person.hello("world"); // output: "James Smith says hello world"
person.hello.call({ name: "Jim Smith" }, "world"); // output: "Jim Smith says hello world"
Bind将它附加到函数中,需要像这样单独调用:
var person = {
name: "James Smith",
hello: function(thing) {
console.log(this.name + " says hello " + thing);
}
}
person.hello("world"); // output: "James Smith says hello world"
var helloFunc = person.hello.bind({ name: "Jim Smith" });
helloFunc("world"); // output: Jim Smith says hello world"
或者像这样:
...
var helloFunc = person.hello.bind({ name: "Jim Smith" }, "world");
helloFunc(); // output: Jim Smith says hello world"
Apply类似于call,只是它接受一个类似数组的对象,而不是一次列出一个参数:
function personContainer() {
var person = {
name: "James Smith",
hello: function() {
console.log(this.name + " says hello " + arguments[1]);
}
}
person.hello.apply(person, arguments);
}
personContainer("world", "mars"); // output: "James Smith says hello mars", note: arguments[0] = "world" , arguments[1] = "mars"