letconst

Letconst is an informal term used in JavaScript discussions to describe the practice of choosing between the two block-scoped declaration keywords let and const according to intent. It is not a separate syntax or feature of the language; rather, it reflects how developers apply the existing keywords introduced in ES6 to manage variable bindings safely and clearly.

In JavaScript, both let and const are block-scoped, unlike var. The difference is in mutability of the binding: a let binding can be reassigned to a new value, whereas a const binding cannot be reassigned after initialization. However, const does not make objects immutable; properties of a const object can still be changed, and arrays can be modified (for example, pushed or popped) even when the array variable is declared with const.

Practical guidelines: default to const when you do not need to rebind the variable. Use let only when you know the value will change. For example, loop counters and values computed over time commonly use let. When dealing with objects or arrays that will be mutated, declare them with const and modify their contents rather than rebinding the variable.

Browser and tooling support: let and const have been supported in all modern environments since around 2015; older browsers require transpilation. The letconst approach emphasizes predictable bindings, helps avoid accidental reassignments, and aligns with many style guides that encourage default const usage and selective let.