What is the difference between var and let in javascript mcq?

In the early days of JavaScript, there was only one way of declaring variables and that was using the var keyword. A variable declared with var is defined throughout the program. One of the issues with using the var keyword was redeclaring a variable inside a block will also redeclare the variable outside the block. 

With the introduction of ES6 in 2015 two more keywords, let and const came into the picture. var and let are both used for variable declaration in javascript but the difference between them is that var is function scoped and let is block scoped. Variable declared by let cannot be redeclared and must be declared before use whereas variables declared with var keyword are hoisted. 

An example will clarify the difference even better 

Example 1: Here we will see the use of var.

Javascript

    console.log[x];

    var x=5;

    console.log[x];

Output:

undefined
5 

Example 2:  Here we will see the use of let.

Javascript

    console.log[x];

    let x=5;

    console.log[x];

Output:

ReferenceError: Cannot access 'x' before initialization

 Code 1: Let’s see the code in JavaScript.

Javascript

    var x = 5;

    document.write[x, "\n"];

    let y = 10;

    document.write[y, "\n"];

    document.write[z, "\n"];

    var z = 2;

    document.write[a];

    let a = 3;

Output:

Code 2: In the following code, clicking start will call a function that changes the color of the two headings every 0.5sec. The color of the first heading is stored in a var and the second one is declared by using let. Both of them are then accessed outside the function block. Var will work but the variable declared using let will show an error because let is block scoped. 

Javascript

GeeksforGeeks

GeeksforGeeks

Start

    function colour[] {

        setInterval[function[] {

            if [document.getElementById['var'].style.color == 'black']

                var col1 = 'blue';

            else

                col1 = 'black';

            if [document.getElementById['let'].style.color == 'black'] {

                let col2 = 'red';

            } else {

                col2 = 'black';

            }

            document.getElementById['var'].style.color = col1;

            document.getElementById['let'].style.color = col2;

        }, 500];

    }

Output:

JavaScript is best known for web page development but it is also used in a variety of non-browser environments. You can learn JavaScript from the ground up by following this JavaScript Tutorial and JavaScript Examples. 

Let us understand the differences in a tabular form:

var

We have an article on how to declare variables in different ways in JavaScript.

What is the difference between VAR and let in JavaScript?

What is the difference between VAR and let keyword in JavaScript Mcq?

What is the difference between const and let keyword Mcq?

What is difference between LET and VAR in TypeScript?