@typescript-eslint/no-loop-func

A function keeps the variable it uses, not the value the variable had when the function was created. If a loop creates functions that use a var, or a let declared outside the loop, and the loop changes that variable, every one of them sees the last value.

A const never changes, and a let declared in the loop is new in each iteration, so both are safe. A function that's called right where it's written isn't reported either.

This rule is deprecated. Use no-loop-func instead.

Examples#

Reported:

const handlers: Array<() => void> = [];

for (var i = 0; i < 3; i++) {
  handlers.push(() => console.log(i)); // 3, 3, 3
}

const prices = [5, 10, 20];
const totals: Array<() => number> = [];
let total = 0;

for (const price of prices) {
  total += price;
  totals.push(() => total); // 35, 35, 35
}

Not reported:

const handlers: Array<() => void> = [];

for (let i = 0; i < 3; i++) {
  handlers.push(() => console.log(i)); // 0, 1, 2
}

const prices = [5, 10, 20];
const totals: Array<() => number> = [];
let total = 0;

for (const price of prices) {
  total += price;
  const soFar = total;
  totals.push(() => soFar); // 5, 15, 35
}