JS checks whether the form input is empty

JS checks whether the form input is empty

This article mainly introduces the sample code for determining whether the form input is empty in JS. If you need it, you can refer to it for help.

The Code is as follows:

// Remove the spaces on both sides of the input string

 

Function trim (s ){

Var count = s. length;

Var st = 0; // start

Var end = count-1; // end

 

If (s = "") return s;

While (st <count ){

If (s. charAt (st) = "")

St ++;

Else

Break;

}

While (end> st ){

If (s. charAt (end) = "")

End --;

Else

Break;

}

Return s. substring (st, end + 1 );

}

 

 

Suppose the form is like this:

The Code is as follows:

<Form action = "testnew.html" name = "form1">

 

Username: <input type = "text" name = "name">

 

Password: <input type = "password" name = "pwd"> <br>

 

<Input type = "submit" value = "submit" onclick = "isEmpty ()">

 

</Form>

 

 

The function can be defined as follows to determine whether the input is null:

The Code is as follows:

Function isEmpty (){

// Form1 is the name attribute in form

Var _ form = document. form1;

 

If (trim (_ form. name. value) = ""){

Alert ("the user name cannot be blank! ");

Return false;

}

If (trim (_ form. pwd. value) = ""){

Alert ("the password cannot be blank! ");

Return false;

}

 

Return true;

 

}