Suggest to use const (prefer-const)

If a variable is never modified, using the const declaration is better.

const declaration tells readers “this variable is never modified”, reduces what they must think. So it will improve maintainability.

Rule Details

This rule is aimed to flag variables that are declared using let keyword, but never modified after initial assignment.

The following patterns are considered warnings:

let a = 3;
console.log(a);

for (let i in [1,2,3]) { // `i` is re-defined (not modified) on each loop step.
    console.log(i);
}

for (let a of [1,2,3]) { // `a` is re-defined (not modified) on each loop step.
    console.log(a);
}

The following patterns are not considered warnings:

let a; // there is not the initializer.
console.log(a);

for (let i = 0, end = 10; i < end; ++i) { // `end` is never modified, but we cannot separate the declaration without changing the scope.
    console.log(a);
}

var a = 3; // suggest to use `no-var` rule.
console.log(a);

When Not to Use It

If you don’t want to be notified about variables that are never modified after initial assignment, you can safely disable this rule.

Version

This rule was introduced in ESLint 0.23.0.

Resources