JavaScript Let vs Const vs Var – What’s the Difference?

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In JavaScript, let and const are two ways to declare variables. var is the third and the oldest way to declare variables in JavaScript. Here is a brief comparison of the three:

  • let : This keyword is used to declare variables that are meant to be reassigned later. It is similar to var in functionality, but let is block-scoped rather than function-scoped.
  • const : This keyword is used to declare variables that are meant to be read-only. The value of a const variable cannot be reassigned. A const variable must be assigned a value when it is declared.
  • var : This keyword is used to declare variables that are meant to be reassigned later. It is the oldest way to declare variables in JavaScript and is function-scoped, meaning that it is visible within the function it is declared or in the global scope if declared outside of a function.

Here is an example of how you can use let and const:

let x = 10;
console.log(x);  // 10
x = 20;
console.log(x);  // 20

const y = 30;
console.log(y);  // 30
y = 40;  // This will throw an error because y is a const and cannot be reassigned

It’s generally recommended to use const by default, and only use let if you need to reassign the value of a variable. Using var is generally not recommended because let and const are more modern and have better scoping behavior.

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