A brief analysis of JavaScript events and methods_javascript skills

Click a hyperlink to trigger an event

1. Use onclick of a tag

This way of writing has a drawback, that is, after clicking, the page will be refreshed and returned to the top of the page.

How to do it without refreshing?

Copy code The code is as follows:

2. The difference between # and javascript: void (0)

When the hyperlink is a "dead link", use the difference between # and javascript:void(0);.

Void(0) is a useless value, it won’t go anywhere, it has no meaning

And # will refresh the current page.

3. Alternatively, use the href of the a tag

Only the JavaScript in the href of the hyperlink needs to add "javascript:",

Because it is not an event, but treats "javascript:" as a network protocol like "http:", "ftp:", "thunder://", "ed2k://", and "mailto:", Handed over to js parsing engine for processing.

Special emphasis on methods

1. Do not start a new line

Generally when writing braces in js, they should be followed directly instead of starting a new line,

The reason is that js will automatically add a "semicolon" at the end of the statement. If the braces are placed on a new line, the "semicolon" will be automatically added after the return statement, and the return value will become undefined.

2. No need to declare the return value type

No need to declare return value type or parameter type. Function definitions begin with function.

JavaScript does not require all paths to have return values ​​like C# and Java. If there is no return value, it is undefined.

3. No method overloading

There is no method overloading in JavaScript.

Writing parameters in methods is called named parameters

The user calls a method that calculates the sum of multiple numbers. How to get the number of parameters in the method?

Please use arguments object!

Anonymous function

1. Method 1

Copy code The code is as follows:

var f1=function(p1,p2){ return p1 p2; };//Assign the function to a variable

Anonymous functions cannot be called and can only be assigned to a variable. Since it is an assignment statement, a semicolon must be added after it

Application:

Copy code The code is as follows:

document.getElementById(‘btn’).onclick=function(){}

2. Method 2

Copy code The code is as follows:

(function(p1,p2){alert(p1 p2);})(20,30);

3. Method 3

Copy code The code is as follows:

var m1=new Function(“p1”,”p2”,”p3”,”return p1 p2 p3”);
alert(m1(1,2,3));low performance

There are many uses of this kind of anonymous function in jQuery

Extension method prototype

Set the extension method through the prototype of the class object,

The declaration of the extension method must be executed before using the extension method. JS functions do not have special function default value syntax, but you can not pass a value to the parameter. The parameter value without passing a value is undefined. You can make your own judgment to set the default value.

Copy code The code is as follows:

var msg ='xiaoming@111.com';
String.prototype.isEmail = function(){
return this.indexof('@')!= -1 ?true:false;
};
alert(msg.isEmail);

Event

1. Call event

2. Register event

Only after the page is loaded can events be registered for the elements of the page.

So onload = function(){

//Register event here

};

Page load event

Copy code The code is as follows:

The above is the entire content of this article. I hope it can give everyone a new understanding of JavaScript events and methods