Literal constructor

This warning category is spelled [literal-constructors] by qmllint.

Do not use function as a constructor

What happened?

A literal construction function was used as a constructor.

Why is that bad?

Calling a literal construction function such as Number as a regular function coerces the passed value to a primitive number. However, calling Number as a constructor returns an object deriving from Number containing that value. This is wasteful and likely not the expected outcome. Moreover, it may lead to unexpected or confusing behavior because of the returned value not being primitive.

Example

import QtQuick

Item {
    function numberify(x) {
        return new Number(x)
    }
    Component.onCompleted: {
        let n = numberify("1")
        console.log(typeof n)   // object
        console.log(n === 1)    // false

        if (new Boolean(false)) // All objects are truthy!
            console.log("aaa")  // aa
    }
}

To fix this warning, do not call these functions as constructors but as regular functions:

import QtQuick

Item {
    function numberify(x) {
        return Number(x)
    }
    Component.onCompleted: {
        let n = numberify("1")
        console.log(typeof n)   // number
        console.log(n === 1)    // true

        if (Boolean(false))
            console.log("aaa")  // <not executed>
    }
}