Function type of JavaScript reference data type
(1) Create function
var add = function(x,y){
return x+y;
};
console.log(add(10,10));//20
(2) The js function is not overloaded
function sum(x,y){
return x+y+',执行函数1。。。。';
}
function sum(x,y){
return x+y+',执行函数2。。。。';
}
console.log(sum(10,10)); //20,执行函数2。。。。
(3) As a function of value
function callSomeFunction(someFunction,someArg){
return someFunction(someArg) //返回一个函数和参数add10(20)
}
function add10(num){
return num+10;
}
console.log(callSomeFunction(add10,20)); //函数add10()作为参数传入callSomeFunction()
(4) Function internal attributes: arguments, this, caller
1. Arguments: Save parameters. arguments is an array-like object, and its attribute callee is a pointer pointing to the function that owns this arguments object, that is, f()
function f(num){
if(num<=1) return 1;
else return num*arguments.callee(num-1);
}
console.log(f(5));//120
5 f(4)=5 4 f(3)=5 4 3 f(2)=5 4 3 2 f(1)=5 4 3 2 2*1=120
2、this
window.color = 'red'
var obj = {
color:'blue'}
function sayColor(){
console.log(this);
}
sayColor(); //this是widow全局对象
obj.sayColor = sayColor;
obj.sayColor(); //this是对象obj的执行环境对象
3. caller: holds a reference to the function that calls the current function (the function that calls this function)
function outer(){
inner();
}
function inner(){
console.log(inner.caller);//ƒ outer() {inner();}
console.log(arguments.callee.caller);//访问相同信息 ƒ outer() {inner();}
}
outer();
(5) Function attributes: length, prototype
1. length: the number of named parameters the function hopes to receive.
console.log(sum.length);
2. Prototype: saves the real location of all instance methods. It is not enumerable in E5, so it cannot be discovered using for-in.
console.log(sum.prototype);
(6) Function methods: apply(), call(), bind()
Set the value of the object in the function body (change the pointer of this inside the function body)
1. apply() passes in parameters: this+parameter array
function callSum1(n1,n2){
return sum.apply(this,arguments);
}
function callSum2(n1,n2){
return sum.apply(this,[n1,n2]);
}
2. call() passes in parameters: this + multiple parameter values
function callSum3(n1,n2){
return sum.call(this,n1,n2)
}
function callSum4(n1,n2){
return sum.cal(this,arguments[0],arguments[1])
}
console.log(callSum1(10,20));
console.log(callSum2(20,20));
console.log(callSum3(10,40));
console.log(callSum4(20,40));
3. bind() incoming parameters: specify the this value of the bound function
window.color = 'red'
var obj = {
color:'blue',name:'HNN'}
function sayColor(){
console.log(this.color);
}
var objSayColor = sayColor.bind(obj) //绑定函数的this值为obj后执行 <==> sayColor.bind(obj)()
objSayColor() //blue this=>obj
sayColor() //red this=>window
4. Function: Expand the scope in which the function operates
function People(name,age){
this.name = name;
this.age = age;
console.log(this);
}
function Student(name,age,grade){
People.call(this,name,age) //this代表Student，使用Student调用People中的方法，将name,age参数传过去
this.grade = grade;
console.log(this);
}
var stu = new Student('小明',18,'大三');
console.log(stu.name+","+stu.age+","+stu.grade);//小明,18,大三