JavaScript Var

JavaScript has a keyword called "var" which is used to declare variables. Variables are used to store data in your code and can be used to represent values that may change throughout the program. In this tutorial, we will cover the basics of how to use the "var" keyword to declare variables in JavaScript and some of the important features of variables declared with "var".

The basic syntax of declaring a variable with "var" is as follows:

1var variableName = value;

Here, "variableName" is the name of the variable and "value" is the value that you want to assign to the variable. For example, you can declare a variable called "x" and assign it the value of 10 like this:

1var x = 10;

One of the main features of variables declared with "var" is that they are function-scoped. This means that they are accessible within the entire function in which they are declared. If you declare a variable inside a function, it will only be accessible within that function and cannot be accessed outside of it.

1function myFunction(){
2    var x = 10;
3}
4console.log(x); //ReferenceError: x is not defined

Another feature of variables declared with "var" is that they are hoisted to the top of their scope. This means that when you use "var" to declare a variable, you can access it before you declare it in your code.

1console.log(x); //undefined
2var x = 10;

A third feature of variables declared with "var" is that they can be declared multiple times in the same scope. This means that you can declare a variable with the same name multiple times in the same function or block of code.

1var x = 10;
2var x = 20; //no error

Note: Variables declared with "var" are function-scoped, hoisted to the top of their scope, and can be declared multiple times in the same scope. While "var" is widely used in the old JavaScript code, its better to use "let" and "const" for variable declaration as they give more control over variable scope and prevent variable redeclaration.