Double vs. Single Equal Sign

Thursday Sep 17th 1998 by Joe Burns
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Look at a rather small but quite important command, the equal sign.

Hey, Tip Types...

Let's tear this one apart. Today we're going to look at a rather small but quite important command, the equal sign.

Let's take a quick look at the script again:

 

<SCRIPT LANGUAGE="javascript">
<!--Hide the Script

//This Script written by Joe Burns, Ph.D. 
//Use it freely

if (navigator.appname == "Netscape")
{parent.location="nspage.html"} 

else

{parent.location="msiepage.html"}

// End hiding the Script--> 
</SCRIPT> 
 

 

I want you to look at two uses of the equal sign within the script:

 


(navigator.appname == "Netscape") 
and
 

{parent.location="nspage.html"} 

Notice the first use of the equal sign doubles it up and the second is the more traditional single equal sign. Now, to us humans, one or two equal signs don't make for a big difference, but to a JavaScript-reading computer, it signifies a great deal of difference.

Without getting into a lot of programming mumbo jumbo, here's the basic difference (and this always did seem backward to me).

  • A double equal sign means "is equal to."
    Notice the line above involving the double equal sign? It is saying if the navigator application name is equal to Netscape.

  • A single equal sign means "is."
    I'm sure there's a better way of putting it, but that's how I keep it all straight. Notice the line above that uses the single equal sign? It is saying the parent location is nspage.html.

You'll also see a single equal sign being used to denote variables and the like. Just keep it all straight by remembering that only the double equal sign means "is equal to" and the single equal sign can be roughly translated into "is."

That should help you keep it all straight, too.

Next Time: The IF/ELSE Condition

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