Expression: It is a collection of operands and operators

Example: a=a+b;

Operator: An operator is a kind of expression-related thing that operates on operands.

Variable :

• Variables are used to store the data.
• to declare a variable in JavaScript with the help of the var, let, and const keywords.
• The let and const keywords were introduced in the ES6 version.
• Example: integer, string, Boolean, array.

Rules :

• Variable names contain only A-Z, a-z, numbers, and underscore symbols.
• Variables should not start with digits. Variable names are case-sensitive.
• can't use reserved keywords like while, for, if, etc.
• Use descriptive, relevant names instead of a, b, or abs, etc.
• Use camelcase pattern.

Variable declaration :

Syntax: Var variable_name;

Example: var name ;