javascript interview material

What are Variables?

Variables are containers for storing data (storing data values).

3 Ways to Declare a JavaScript Variable

  • Using var
  • Using let
  • Using const

When to Use JavaScript var?

  • Always declare JavaScript variables with var,let, orconst.
  • The var keyword is used in all JavaScript code from 1995 to 2015.
  • The let and const keywords were added to JavaScript in 2015.
  • If you want your code to run in older browsers, you must use var

When to Use JavaScript const?

  • If you want a general rule: always declare variables with const.
  • If you think the value of the variable can change, use let.

JavaScript Identifiers ?

All JavaScript variables must be identified with unique names.
These unique names are called identifiers.
JavaScript identifiers are case-sensitive.

The general rules for constructing names for variables (unique identifiers) are:

  • Names can contain letters, digits, underscores, and dollar signs.
  • Names must begin with a letter.
  • Names can also begin with $ and _ (but we will not use it in this tutorial).
  • Names are case sensitive (y and Y are different variables).
  • Reserved words (like JavaScript keywords) cannot be used as names.

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