Four ways to call named functions in javascript Recommended page 1/3_javascript skills

There is no difference in the execution results of the four methods. But if the function has a return value, you may be a little disappointed when calling it with new.

1. () parentheses operator The most commonly used one is the () operator to call a function

Copy code The code is as follows:

//No parameter function fun1
function fun1() {
alert('I was called');
}
fun1()

/ / Function fun2 with parameters
function fun2(param) {
alert(param);
}
fun2('I was called')

After adding call and apply to Function after ECMAScript 3, there are two types of
2. call

Copy code The code is as follows:

//No parameter function fun1
function fun1() {
alert('I was called');
}
fun1.call(null);

//Function fun2 with parameters
function fun2(param) {
alert(param);
}
fun2.call(null,'I was called')

3. apply

Copy code The code is as follows:

//No parameter function fun1
function fun1() {
alert('I was called');
}
fun1.apply(null);

//Parameter function fun2
function fun2(param) {
alert(param);
}
fun2.apply(null,['I was called'])

4. new (not recommended Use this method )

Copy the code The code is as follows:

//No parameter function fun1
function fun1( ) {
alert('I was called');
}
new fun1();


//function fun2 with parameters
function fun2(param) {
alert(param);
}
new fun2('I was called')

ok, from the above calling method, there are four execution methods There is no difference in the results. But if the function has a return value, you may be a little disappointed when calling it with new.

Copy code The code is as follows:

//Function fun with a return value
function fun() {
alert( 'I was called');
return "jack";
}

var c = new fun();
alert(c);//[object Object], why Not "jack"?

Changed to this,

Copy the codeThe code is as follows:

//There is a return value Function fun
function fun() {
alert('I was called');
return {name:'jack'};
}

var c = new fun();
alert(c.name);//jack, returned normally again

Okay, to summarize: when calling a function using new method. If there is a return value, when the return value is a built-in type (basic type) of JavaScript such as String, Number, Boolean, etc., the value will not be returned; when the return value is an object, function , array and other object types, the object, function, array will be returned.

When the return value is a built-in type (basic type), what exactly does new fun() return? The next article will discuss the details of the new method call.