Example of setting default parameter values in Javascript

The first:

function test(a,b){

var a = arguments[0] ? arguments[0] : 1;//Set the default value of parameter a to 1

var b = arguments[1] ? arguments[1] : 9;//Set the default value of parameter b to 9

return a+b;

The equivalent to

function test(){

var a = arguments[0] ? arguments[0] : 1;//Set the default value of parameter a to 1

var b = arguments[1] ? arguments[1] : 9;//Set the default value of parameter b to 9

return a+b;

}

Invoke the sample

alert(test()); //The output of 10

alert(test(5)); //The output of 14

alert(test(5,6)); //The output of 11

alert(test(null,6)); //The output of 7

alert(test(6,null)); //The output of 15

The second:

function test(blog,address){

blog=blog||' forget ~ Shallow, ';

address=address||'www.jb51.net';

alert(' Blog is '+blog+' The address is '+address);

}

The equivalent to

function test(blog,address){

if(!blog){blog=' forget ~ Shallow, ';}

if(!address){address='www.jb51.net';}

alert(' Blog is '+blog+' The address is '+address);

}

Invoke the sample

test(); //The blog name is forgotten ~ the address is www.jb51.net

test('csdn','blog.csdn.net'); //The blog name is CSDN and the address is blog.csdn.net

test('','blog.csdn.net/u011043843'); // Blog name is forgotten ~ Shallow, 

The third:

function test(setting){

var defaultSetting={

name:' programmer ',

age:'1',

phone:'15602277510',

QQ:'259280570',

message:' You are welcome to join us '

};

$.extend(defaultSetting,setting);

var msg=' Name: '+defaultSetting.name

+' Age: '+defaultSetting.age

+' , telephone: '+defaultSetting.phone

+' . QQ Group: '+defaultSetting.QQ

+' , note: '+defaultSetting.message

+' . ';
alert(msg);
}

Invoke the sample

test(); //Output: name: program lover, age: 1, phone: 15602277510, QQ group: 259280570, description: welcome to join.

test({

name:'dwqs',

age:'20',

QQ:'461147874',

message:' Blog: www.jb51.net'

});

//Output: name: DWQS, age: 20, phone: 15602277510, QQ group: 461147874, description: blog: www.jb51.net.

Ps: this method can be used if the function has many parameters. This is an extension of JQuery, so you need to introduce JQuery.