function printMessage() {
  alert("Hello from External");
}

<SCRIPT LANGUAGE="JavaScript">
document.write('<SCRIPT LANGUAGE="JavaScript" SRC="010226b.js"><\/SCRIPT>');
</SCRIPT>

Now, suppose you want to call the printMessage() function in the main html program, immediately after loading the script:

<SCRIPT LANGUAGE="JavaScript">
document.write('<SCRIPT LANGUAGE="JavaScript" SRC="010226b.js"><\/SCRIPT>');
printMessage();
</SCRIPT>

Try it. You get an error message. The reason for this failure is that both Internet Explorer 5.5 and Netscape 6 do not wait for the external script to be read before continuing parsing the main script.

One of the remedies for this problem is to use indirection. Put a static include in your main program, and then write the dynamic loading command (document.write) in the included file. For example, put the following code in your main page:

<SCRIPT LANGUAGE="JavaScript" SRC="010301b.js"></SCRIPT>

In the file 010301b.js put the dynamic load command:

document.write('<SCRIPT LANGUAGE="JavaScript" SRC="010301c.js"><\/SCRIPT>');

Your main page should like like this now:

<SCRIPT LANGUAGE="JavaScript" SRC="010301b.js"></SCRIPT>
<SCRIPT LANGUAGE="JavaScript">
printMessage();
</script>

Check it out. You should get the alert message "Hello From External."

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