Remove unused variable

Remove a variable that is not read or written.

Remove unused variable

Why is this refactoring helpful?

Unused variables need to be read and understood, even though they have no impact on the program. Removing them makes programs easier to understand.

What do I need to consider?

Global variables could be used in other files.

Top-level var declarations can declare global variables when the file is not a module, and removing such variables could affect their use in other files.

Initial value expressions can have side-effects.

An initial value expression can have side-effects. Consider the following example:

let counter = 0;
function count() {
    return ++counter;
}

const a = count();
const b = count();

console.log(b); // 2

Here, removing the declaration of the unused variable a would change the value of b to 1, because the first count() call would be removed.

Object destructuring can have side-effects.

Getters can have side-effects that are invoked when destructuring an object.

Array destructuring can have side-effects.

Array destructuring can be invoked on any iterable, and custom iterable implementations could have side-effects.

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