JavaScript Keywords and Identifiers

JavaScript Keywords

Keywords are reserved words that are part of the syntax in the programming language. For example,

const a = 'hello';

Here, const is a keyword that denotes that a is a constant.

Keywords cannot be used to name identifiers.

Here is the list of keywords available in JavaScript.

JavaScript Identifiers

An identifier is a name that is given to entities like variables, functions, class, etc.

Rules for Naming JavaScript Identifiers

The rules for writing identifiers are:

• Identifier names must start with either a letter, an underscore _, or the dollar sign $. For example,

  //valid
  const a = 'hello';
  const _a = 'hello';
  const $a = 'hello';

• Identifier names cannot start with numbers. For example,

  //invalid
  const 1a = 'hello'; // this gives an error

• JavaScript is case-sensitive. So y and Y are different identifiers. For example,

  const y = "hi";
  const Y = 5;
  console.log(y); // hi
  console.log(Y); // 5

• Keywords cannot be used as identifier names. For example,

  //invalid
  const new = 5; // Error! new is a keyword.