Difference between JavaScript variable keyword (var, let, const)

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Before ECMAScript 2015, JavaScript had only one variable keyword called var. ECMAScript 2015 introduces us to two new variable keywords known as let and const.

const: If any variables are defined with const, they cannot be reassigned.

Example:

const fruit = ‘Mango’;
fruit = ‘Apple’; // You cannot change the value, which is defined with const, so it will throw an error.

let: it’s a block scoped {}. So, if the variables are defined with let, it will only work within a block {}.

// num will not work here, because it is outside the for loop block
for (let num = 0; num < 5; num++) {
// num variable is only work in here
}
// num will not work here, because it is outside the for loop block

var: if the variables are defined with var, they will work inside and outside a block {}.

// num will work in here
for (let num = 0; num < 5; num++) {
// num will work in here
}
// num will work in here