TypeError: calling a builtin X constructor without new is forbidden

The JavaScript exception "calling a builtin X constructor without new is forbidden" occurs when you try to call a builtin constructor without using the {{jsxref("new")}} keyword. All modern constructors, such as {{jsxref("Promise")}} and {{jsxref("Map")}}, must be called with new.

Message#

TypeError: Constructor X requires 'new' (V8-based)
TypeError: Promise constructor cannot be invoked without 'new' (V8-based)
TypeError: calling a builtin X constructor without new is forbidden (Firefox)
TypeError: calling X constructor without new is invalid (Safari)

Error type#

{{jsxref("TypeError")}}

What went wrong?#

In JavaScript, calling a function without new and constructing a function with new are two distinct operations, and functions can behave differently depending on how they are called.

Apart from the following legacy constructors, all modern constructors must be called with new:

• {{jsxref("Object/Object", "Object()")}}
• {{jsxref("Function/Function", "Function()")}} (and its subclasses)
• {{jsxref("Error/Error", "Error()")}} (and its subclasses)
• {{jsxref("RegExp/RegExp", "RegExp()")}}
• {{jsxref("Array/Array", "Array()")}}

Some other constructors, such as {{jsxref("Date/Date", "Date()")}}, and primitive wrappers, such as {{jsxref("String/String", "String()")}}, {{jsxref("Number/Number", "Number()")}}, and {{jsxref("Boolean/Boolean", "Boolean()")}}, can also be called with or without new, but the return types differ in the two cases.

On every constructor page, you can find information about whether the constructor must be called with new.

Examples#

Invalid cases#

```js example-bad const m = Map(); // TypeError: calling a builtin Map constructor without new is forbidden

### Valid cases

```js example-good
const m = new Map();

See also#

• {{jsxref("new")}}