Invalid Constructor Usage

ID

javascript.invalid_constructor_usage

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

JavaScript

Tags

classes, reliability, runtime-error

Description

Reports a new X() expression whose target is a function that cannot be used as a constructor at runtime:

const fn = () => ({ x: 1 });
const obj = new fn();              // FLAW — TypeError at runtime

async function load() { ... }
const r = new load();              // FLAW — async functions are not constructors

function* gen() { yield 1; }
const g = new gen();               // FLAW — generators are not constructors

Rationale

The JavaScript runtime distinguishes between functions that can be invoked with new and those that cannot:

  • arrow functions have no slot,

  • async functions return a Promise; their internal slot does not support new,

  • generator functions return a generator object; the runtime rejects new.

In every case the call throws a TypeError. The rule catches the bug at static analysis time, before it surfaces as a runtime exception in production.

Remediation

Use the function as a regular call, or change the declaration to a normal function or class if construction is the intent:

const obj = fn();

class Foo { ... }
const obj = new Foo();

Notes

The check resolves the identifier to its declaration through sankxy’s symbol table. If the declaration is a regular function or a class, no issue is reported. If the identifier cannot be resolved (e.g. it comes from an unanalysed import) the rule stays silent.

References