JavaScript for...in loop

There is one more loop supported by JavaScript. It is called for...in loop. This loop is used to loop through an object's properties.

Because we have not discussed Objects yet, so you may not feel comfortable with this loop. But once you will have understanding on JavaScript objects then you will find this loop very useful.

Syntax:

for (variablename in object){ statement or block to execute }

In each iteration one property from object is assigned to variablename and this loop continues till all the properties of the object are exhausted.

Example:

Here is the following example that prints out the properties of a Web browser's Navigatorobject:

<script type="text/javascript"> <!-- var aProperty; document.write("Navigator Object Properties<br /> "); for (aProperty in navigator) { document.write(aProperty); document.write("<br />"); } document.write("Exiting from the loop!"); //--> </script>

This will produce following result:

Navigator Object Properties appCodeName appName appMinorVersion cpuClass platform plugins opsProfile userProfile systemLanguage userLanguage appVersion userAgent onLine cookieEnabled mimeTypes Exiting from the loop!