var-used-in-block-scope.qdoc

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// Copyright (C) 2023 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
\page qmllint-warnings-and-errors-block-scope-var-declaration.html
\ingroup qmllint-warnings-and-errors
 
\title Block scope var declaration
\brief [var-used-in-block-scope] A variable has been declared with var inside a block scope
 
\qmllintwarningcategory block-scope-var-declaration
 
\section1 A variable has been declared with var inside a block scope
 
\section2 What happened?
A JavaScript variable has been declared with var inside of a block scope, for
example in the body of a while loop.
While it might look like the variable is only usable inside that scope, it
can actually be accessed outside of it, as it is hoisted to the scope of the
innermost function or QML binding.
 
\section2 Why is this bad?
It can be confusing to track the scope of such a variable, and they might
accidentally shadow other variables.
 
\section2 Example
\qml
import QtQuick
 
Item {
    id: root
    property int count: 0
    function countItems() {
        let sum = 0
        {
            var count = root.children.length
            sum += count
        }
        // ... more additions to sum
        count = sum // modifies the function local variable, not root.count
    }
}
\endqml
To fix this warning, use let or const instead, or declare the variable directly in the function scope.
\qml
import QtQuick
 
Item {
    id: root
    property int count: 0
    function countItems() {
        let sum = 0
        {
            let count = root.children.length
            sum += count
        }
        // ... more additions to sum
        count = sum // modifies the function local variable, not root.count
    }
}
\endqml
*/