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

In JavaScript, the keyword used to declare a variable is "var." This keyword has been part of the language since its inception and allows developers to create variables that may be reassigned, meaning that the value of the variable can change as the program executes.

When you declare a variable using "var," it is function-scoped or globally scoped, depending on where it's declared. This means that if you declare a variable inside a function using "var," it can only be accessed within that function. If declared outside of any function, it becomes a global variable accessible throughout the entire script.

The other options listed do not represent valid keyword syntax for declaring variables in JavaScript. "vars" and "types" are not recognized keywords, which could lead to errors if used in a script. "type" is also not relevant to variable declaration and is associated with data types in programming languages, not specifically with variable declaration in JavaScript. Therefore, "var" is the correct choice, as it accurately reflects the proper way to declare a variable in the language.