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>
     }
 }

Array has confusing semantics

What happened?

An Array constructor was used with more than one argument.

Why is that bad?

The Array constructor has confusing semantics:

• new Array() creates an empty array.
• new Array(42) creates an array with 42 elements.
• new Array(42, 43) creates an array with two elements, 42 and 43.

Example

 import QtQuick

 Item {
     function createArray() {
         return new Array(1, 2, 3)
     }
 }

To fix this warning, use [...] instead of new Array(...).

functions:

 import QtQuick

 Item {
     function createArray() {
         return [1, 2, 3]
     }
 }