no-unused-vars

NOTE: this rule is part of the recommended rule set.

Enable full set in deno.json:

{
  "lint": {
    "rules": {
      "tags": ["recommended"]
    }
  }
}

Enable full set using the Deno CLI:

deno lint --rules-tags=recommended

This rule can be explictly included to or excluded from the rules present in the current tag by adding it to the include or exclude array in deno.json:

{
  "lint": {
    "rules": {
      "include": ["no-unused-vars"],
      "exclude": ["no-unused-vars"]
    }
  }
}

Enforces all variables are used at least once.

If there are variables that are declared but not used anywhere, it's most likely because of incomplete refactoring. This lint rule detects and warns such unused variables.

Variable a is considered to be "used" if any of the following conditions are satisfied:

its value is read out, like console.log(a) or let otherVariable = a;
it's called or constructed, like a() or new a()
it's exported, like export const a = 42;

If a variable is just assigned to a value but never read out, then it's considered to be "not used".

let a;
a = 42;

// `a` is never read out

If you want to declare unused variables intentionally, prefix them with the underscore character _, like _a. This rule ignores variables that are prefixed with _.

Invalid:

const a = 0;

const b = 0; // this `b` is never used
function foo() {
  const b = 1; // this `b` is used
  console.log(b);
}
foo();

let c = 2;
c = 3;

// recursive function calls are not considered to be used, because only when `d`
// is called from outside the function body can we say that `d` is actually
// called after all.
function d() {
  d();
}

// `x` is never used
export function e(x: number): number {
  return 42;
}

const f = "unused variable";

Valid:

const a = 0;
console.log(a);

const b = 0;
function foo() {
  const b = 1;
  console.log(b);
}
foo();
console.log(b);

let c = 2;
c = 3;
console.log(c);

function d() {
  d();
}
d();

export function e(x: number): number {
  return x + 42;
}

export const f = "exported variable";

no-unused-vars

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