Unused variable in for each

Question

I have this function in my TS project:

  size(): number {
    let size = 0;
    for (const _ of this) {
      size++;
    }

    return size;
  }

While I want to continue using a for each to count the elements I get following eslint error:

'_' is assigned a value but never used

In other languages like ruby, prefixing with an underscore would fix this. In this case that doesn't work.

Answer 1

You can configure your ESLint no-unused-vars rule to add a varsIgnorePattern, e.g. ^_ for “starts with underscore”:

"no-unused-vars": ["error", {
  "varsIgnorePattern": "^_"
}]

Alternatively, you can suppress the error on the code side, e.g. with the void operator (an idiomatic way of discarding the result of any expression) as @JaromandaX commented:

size(): number {
  let size = 0;
  for (const _ of this) {
    void _;
    size++;
  }

  return size;
}

ESLint also has a general mechanism for inline rule configuration.