Javascript is a case-sensitive language.
The keyword in javascript must be small letters, "if","switch","case","catch", cannot be written as "If","Switch","Case","Catch".
And when you define and use variable name, function name in javascript, their case must be consistent.
The confused fact is HTML is non case-sensitive language, so tags and properties can be written in any case.
For example, the onload function of html body, can be written as <body onLoad="doSth();">, but if you want to set the body's onload function in javascript, it'd better be written as "onload":
<script language="javascript">
//......
this.onload = doSth();
//......
</script>
