JS-002
JavaScript diagram about let vs const: a visual example of Can the value change
Beginner3 min~3 min read#let#const#variables

let vs const

Can the value change?

Goal

Understand when to use let and when to use const.

Explanation

  • JavaScript offers two modern ways to create variables.
  • const means the variable must always refer to the same value.
  • let means you can change the value later.
  • If you do not plan to change anything — use const.
  • If the value will change while the program runs — use let.

Analogy

const is a locked box. let is a regular box you can open and change what is inside.

Code

let score = 10;

score = 20;

const age = 30;

// age = 31 ❌

Result: TypeError: Assignment to constant variable.

Common mistake

Many people think const makes data completely immutable. In reality, it only prevents reassigning the variable itself.

Remember

  • ✦ let can be changed.
  • ✦ const cannot be reassigned.
  • ✦ Use const by default.

Quick Quiz

Which variable should you use by default?

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