External JavaScript Not Running, does not write to document

I'm trying to use an external JavaScript file in order to write "Hello World" into a HTML page.

However for some reason it does not work, I tried the same function and commands inline and it worked, but not when it's using an external JavaScript file. The part I commented out in the JS file was the previous method I was trying to use. Those lines of could worked when I ran the script from the header, and inline. Thanks

Html file:

<html>

    <head>
    </head>

<body>

    <p id="external">

        <script type="text/javascript" src="hello.js">
            externalFunction();
        </script>
    </p>

    <script type="txt/javascript" src="hello.js"></script>

</body>

</html>

JavaScript file

function externalFunction() 
        {
         var t2 = document.getElementById("external");

            t2.innerHTML = "Hello World!!!"

         /*document.getElementById("external").innerHTML = 
         "Hello World!!!";*/

        }

In general, you want to place your JavaScript at the bottom of the page because it will normally reduce the display time of your page. You can find libraries imported in the header sometimes, but either way you need to declare your functions before you use them.

http://www.w3schools.com/js/js_whereto.asp

index.html

<!DOCTYPE html>
<html>

<head>
  <!-- You could put this here and it would still work -->
  <!-- But it is good practice to put it at the bottom -->
  <!--<script src="hello.js"></script>-->
</head>

<body>

  <p id="external">Hi</p>

  <!-- This first -->
  <script src="hello.js"></script>

  <!-- Then you can call it -->
  <script type="text/javascript">
    externalFunction();
  </script>

</body>

</html>

hello.js

function externalFunction() {
  document.getElementById("external").innerHTML = "Hello World!!!";
}

Plunker here.

Hope this helps.

Script tags with SRC values do not run the contents. Split it to two script tags. One for the include, one for the function call. And make sure the include is before the call.

use onload eventListener to make it simple

<script>
   window.onload = function() {
      externalFunction();
   }
</script>

ZeroBased_IX

You're trying to call the function before it has been loaded.

Place the load script above the declaration:

<html>

    <head>
<script type="txt/javascript" src="hello.js"></script>
    </head>

<body>

    <p id="external">

        <script type="text/javascript">
            externalFunction();
        </script>
    </p>



</body>

</html>

Also you have a typo:

 <script type="txt/javascript" src="hello.js"></script>

Should be:

<script type="text/javascript" src="hello.js"></script>

The script type needs to be "text/javascript" not "txt/javascript".

来源：https://stackoverflow.com/questions/26821566/external-javascript-not-running-does-not-write-to-document

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external