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To run a .js file

node <filename>.js

let in JavaScript is used to declare a variable. It is similar to var but has some differences.

let name = "john";

console.log("Hello " + name + "!");

const keyword in JavaScript is used to declare a constant variable. The value of a constant variable cannot be changed once it is assigned.

const name = "john";
name = "doe";

console.log("Hello " + name + "!");