Javascript form validation

I am doing some basic form validation.

I have the following javascript function

function fullField(x,span_id)
{
var result=false;
if(x.value==0)
{
    document.getElementById(span_id).innerHTML =" Required";
    result=false;
}else{
    document.getElementById(span_id).innerHTML="";//can use tick <img src='images/site_images/tick.png' />
    result=true;
}

return result;
}

I have an input which is checked onblur

<input type='text' onblur='return fullField(this,'span1')name='first_name' />
<span id='span1'></span>

The function works, writing 'Required' into the span if the person tabs off the field without filling it in. However, when i click submit the form still submits. I think i am missing some fundamental point here because i though that if any of the fields in my form return false then the form would not submit. Is the only way to get around this to check the entire form again onsubmi开发者_开发技巧t?

You could create a variable on the page that will be set to false if validation on a field fails and then for the form onSubmit(return(myValidationVariable)) - not the most elegant design but should work well with your current setup.