In JavaScript, what keyword is used to declare a variable?

In JavaScript, the keywords used to declare a variable are specifically 'var', 'let', and 'const'. Each of these keywords serves a distinct purpose when declaring variables.

'Var' is the traditional way to declare variables and has function scope, meaning its scope is confined to the function in which it is declared. 'Let' was introduced in ES6 (ECMAScript 2015) and allows block scope, which means variables declared with 'let' are only accessible within the block they are defined (such as within an if statement or for loop). 'Const' is also block-scoped and is used for declaring constants, which means the variable cannot be reassigned after its initial value has been set.

The other terms such as 'declare', 'function', and 'define' do not represent valid keywords for variable declaration in JavaScript. 'Declare' is not a recognized JavaScript keyword, 'function' is used to define functions, and 'define' is not part of the JavaScript syntax for variable creation.