Constants and global variables are always written in uppercase.

The following are the rules for naming variables in JavaScript:

1. Spaces are not allowed in variable names.
2. Only letters, digits, underscores, and dollar signs are permitted in variable names.
3. Case matters when it comes to variable names.
4. A letter (alphabet), an underscore (_), or a dollar sign ($) must be the first character in a variable name, any other special characters must not be taken.
5. certain terms such as reserved words in javascript shouldn’t be used to name variables.