In JavaScript, we can declare a variable in different ways by using different keywords. Each keyword holds some specific reason or feature in JavaScript. Basically, we can declare variables in three different ways by using var, let and const keywords. Each keyword is used in some specific conditions.
|
JavaScript var |
JavaScript let |
JavaScript const |
|---|---|---|
| Can be redeclared | Cannot be redeclared | Cannot be redeclared |
| Can be reassigned a value | Can be reassigned a value | Cannot reassign the value |
| Only have global and function scope | Can have a block scope | Can have a block scope |
| Variables are hoisted on top and can be used anywhere | Variables must be initialized before use | Variables must be initialized before use |
| Can be redeclared anywhere in the program | Can be redeclared inside a block | Can never be redeclared |
JavaScript var: This keyword is used to declare variables globally. If you used this keyword to declare a variable then the variable can accessible globally and changeable also. It is good for a short length of codes, if the codes get huge then you will get confused.
Syntax:
var variableName = "Variable-Value;"
Example:
javascript
<script> var neveropen = "neveropen"; console.log(neveropen);</script> |
Output:
neveropen
JavaScript let: This keyword is used to declare variable locally. If you used this keyword to declare a variable then the variable can accessible locally and it is changeable as well. It is good if the code gets huge.
Syntax:
let variableName = "Variable-Value;"
Example:
javascript
<script>if (true) { let neveropen = "neveropen"; console.log(neveropen); } /* This will be error and show neveropen is not defined */ console.log(neveropen);</script> |
Output:
neveropen
JavaScript const: This keyword is used to declare variable locally. If you use this keyword to declare a variable then the variable will only be accessible within that block similar to the variable defined by using let and difference between let and const is that the variables declared using const values can’t be reassigned. So we should assign the value while declaring the variable.
Syntax:
const variableName = "Variable-Value;"
Example:
javascript
<script> const neveropen = "neveropen"; console.log(neveropen);</script> |
Output:
neveropen