Question

I tried to write a function on a JS file and another function with the same name in the page.
I expected an error but no error came and I got only the function from the JS file to execute.

How is this possible? Even if I write a function in a separate JS file, everything is rendered in a single html file. Then how come it is possible?

<script type="text/javascript" language="javascript" src="JScript.js"></script>
<script language="javascript">
  function Boo() {
    alert("Hai new");
  }
</script>

<button onclick="Boo();">Click</button>

and in the JS file

function Boo() {
  alert("Hai");
}

Answer 1

One aspect that not many people ever think about with JavaScript is
that if you define multiple functions
with the same name then the last one
defined will be the one that actually
runs. JavaScript functions are not
polymorphic the way that functions in
many other languages are in that
JavaScript doesn’t care if the actual
arguments defined for the functions
are different as it can’t distinguish
between them on that basis. Where in
other languages you might have
myfunc(oneparm) and myfunc(parmone,
parmtwo) as two separate functions
with the one that gets run depending
on the number of parameters passed, in
JavaScript the last one defined will
always be the one run regardless of
the number of parameters.

http://javascript.about.com/library/blpolyfunc.htm