Question

I recently learnt this code but this code is not working as it is expected to .It is for form validation

function username_validation(name){
    var valid_name = /^[a-zA-Z0-9_]{5,30}$/;
    if(!valid_name.test(name)) 
     {         
         return false; 
     } 
     else 
     { 
         return true;
     } 


}

Answer 1

You must hook this function to an event listener.
Like :

<form onsubmit="username_validation(this.usernameTextfield.value);">

So this function will be triggered every time that particular form is submitted.
There’s nothing wrong with your function.

The line :

var valid_name = /^[a-zA-Z0-9_]{5,30}$/;

creates a RegExp object.

Then :

valid_name.test(name)

checks if the name mathces with the valid_name pattern.
RegExp has a boolean method test(s) which returns true if the given string s matches with the RegExp pattern

A better way to write that would be :

function validate(name) {
    var r=/^[a-zA-Z0-9_]{5,30}$/;
    return r.test(name);
}

Hope it helps…