JavaScript Reserved Words
Words with a special meaning, such as var, are keywords, and they may not be used as variable names. abstract else instanceof super boolean enum int switch break export interface synchronized byte extends let this case false long throw catch final native throws char finally new transient class float null true const for package try continue function private typeof debugger goto protected var default if public void delete implements return volatile do import short while double in static with The following three identifiers are not reserved words, but you should treat them as if they were: Infinity NaN undefined
JavaScript is often used together with Java. 
Avoid using some Java objects and properties as JavaScript identifiers:
getClass	java	JavaArray	javaClass	JavaObject	JavaPackag

JavaScript can be used outside HTML. It can be used as the programming
language in many other applications.

In HTML you must (for portability you should) avoid using the name of HTML and Windows objects and properties.

js reserved words

HTML Event Handlers
In addition you should avoid using the name of all HTML event handlers. Examples: onblur onclick onerror onfocus onkeydown onkeypress onkeyup onmouseover onload onmouseup onmousedown onsubmit