Explain how to use the for...in statement in JavaScript_Basic knowledge

Here is another loop supported by JavaScript. It's called a for...in loop. This loop is used to loop through the properties of an object.

Using this loop may feel a bit unclear since we don’t have an object to discuss yet. However, once you understand JavaScript objects, you will find this loop very useful.
Grammar

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

Each iteration from the object assigns an attribute to the variable name (variablename), and this loop continues until all attributes of the object are exhausted.
Example:

The following is to print out the properties of the Navigator object of the web browser, as in the following example:

<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 the following results:

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