The importance of JavaScript var

JavaScript's VAR function is to declare variables.

In general, there will be no error, but some cases will have different results if they are not written.

<div id= "A" ></div>  
<script type= "Text/javascript" >  
a = 1;  
alert (a);  
</script>

This example above in the FF Chrome implementation will not be a problem, can output 1. But what about running in IE? Error: "Object doesn ' t support this property or method."

Because IE can get a reference to a DOM element directly by ID, A=1 will make an error because at this point A is the DOM element of id= "a".

If the <div id= "a" ></div> this sentence is removed, there will be no problem. To avoid this conflict, it is recommended that you declare variables with var.

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