Before ES6, JavaScript developers mainly used the var keyword to declare variables. This often caused confusion and bugs because var does not follow proper block scope rules.
ES6 introduced let and const to fix these problems. These new keywords make variable behavior more predictable and code easier to manage.
Understanding let, const, and block scope is essential for writing modern, safe, and professional JavaScript code.
Difference Between var, let, and const
var
- Function scoped
- Can be redeclared
- Can cause unexpected bugs
let
- Block scoped
- Can be reassigned
- Safer than var
const
- Block scoped
- Cannot be reassigned
- Best for values that never change
Modern JavaScript prefers let and const over var.
Here, the variable declared with var is accessible outside the block.
This behavior can cause unexpected bugs in large programs.
The variable declared with let exists only inside the block.
This makes your code safer and easier to control.
These examples show how let and const provide better control over variables compared to var.
By using let and const correctly, students write cleaner, safer, and more professional JavaScript code that follows modern development standards.