What is the difference between let and const in JavaScript?

Both let and const are block-scoped declarations introduced to replace the older var patterns in most modern code. const prevents re-binding a variable to a new value, but does not make objects deep-frozen. let allows reassignment. Teams often default to const to signal intent, then use let when a variable must be reassigned (like an index, accumulator in a loop, or a flag that changes).

const user = { name: 'A' };
user.name = 'B'; // mutating object, not rebinding the variable
// user = {} would throw in strict-like common patterns with const

Start simple: try this concept in a tiny project before moving to advanced tools.