This warning category is spelled [var-used-before-declaration] by qmllint.

Variable is used here before its declaration

What happened?

You used a variable before you declared it.

Why is this bad?

This makes the code harder to read. Variables declared with let or const will error out at runtime.

Example

import QtQuick

Item {
    function f() {
        x = 42; // x is used before its declaration
        let x;
    }

    Component.onCompleted: f()
}

To fix this warning, move the declaration before the usage:

import QtQuick

Item {
    function f() {
        let x;
        x = 42;
    }

    Component.onCompleted: f()
}