To summarize, variables introduced with var have the potential of being affected by hoisting, a mechanism in JavaScript in which variable declarations are saved to memory. OutputUncaught Synta圎rror: Identifier 'y' has already been declared Check if variable is equal to value if (username = 'sammy_shark' ) JavaScript will remember that username represents the string value sammy_shark.

The value being assigned, 'sammy_shark'.

The assignment operation, represented by the = syntax.

The variable name (or identifier), username.The declaration of a variable using the var keyword.Assign the string value Sammy to the username identifier var username = 'sammy_shark' In the example below, we will declare a variable, and assign a value to it. We can use var to demonstrate the concept of a variable itself. We’ll go over the differences between var, let, and const keywords in its own section below. As a result, most older code and learning resources will only use var for variables. Prior to the ECMAScript 2015 (ES6) language specification that today’s JavaScript is based on, there was only one way to declare a variable - using the var keyword. In JavaScript, the value contained inside a variable can be any JavaScript data type, including a number, string, or object.

A piece of information that we might reference multiple times can be stored in a variable for later use or modification.

Understanding VariablesĪ variable is a named container used for storing values. We will also review the effects of hoisting and the significance of global and local scope to a variable’s behavior. This tutorial will cover what variables are, how to declare and name them, and also take a closer look at the difference between var, let, and const. In JavaScript, there are three keywords used to declare a variable - var, let, and const - and each one affects how the code will interpret the variable differently. There are a number of different properties of variables in JavaScript, as well as several rules which must be followed when naming them. Variables are a fundamental part of many programming languages, and are among the first and most important concepts for novice coders to learn.

What is mean in javascript