return value in javascript

I am new to javascript and I am little bit confused about the syntax.

function validateForm()
{
var x=document.forms["myForm"]["fname"].value
if (x==null || x=="")
  {
  alert("First name must be filled out");
  return false;
  }
}

<form name="myForm" action="demo_form.asp" onsubmit="return validateForm()" method="post">
First name: <input type="text" name="fname">
<input type="submit" value="Submit">
</form>

My question is If I write开发者_如何学运维 onsubmit="return validateForm()" or write onsubmit="validateForm()". What's the difference between these two syntax. So I submitted before just an example.

Here it is example

Event = function(); or Event = return function();

What's the difference between these two syntax

They're both invalid.

The return statement should be used within a function. The expression following a return statement is what will be returned from the function, so:

function foo() {
    return 1234;
}

foo(); // => 1234

If you want to assign a function to the Event identifier, then you would do it like so:

Event = function() {
    // function body (what do you want the function to do?)
};

onsubmit="validateForm()" just calls the function and whatever is returned is lost and does not effect anything. But in onsubmit="return validateForm()" the returned value is returned again and if false will not submit the form and if true will continue the submitting process. So you can use it like:

function check()
{
    if(document.getElementByName("fname").value == ""){
        return(false);  //Do not submit the form
    }
    return(true);  //Submit the forum
}

<form name="myForm" action="demo_form.asp" onsubmit="return(check());" method="post">
First name: <input type="text" name="fname">
<input type="submit" value="Submit">
</form>