wrapperObjects

Flags using new with Boolean, Number, or String, which creates wrapper objects instead of primitives.

✅ This rule is included in the ts logical presets.

Using new with Boolean, Number, or String creates object wrappers around primitive values. These wrapper objects behave differently from primitives in surprising ways:

const primitiveString = "hello";
const wrappedString = new String("hello");

primitiveString === "hello"; // true
wrappedString === "hello"; // false - object vs primitive comparison

typeof primitiveString; // "string"
typeof wrappedString; // "object"

Wrapper objects are almost never intended. This rule reports when a wrapper object is created instead of a normal primitive.

Examples

❌ Incorrect

const text = new String("hello");

const count = new Number(42);

const flag = new Boolean(true);

✅ Correct

const text = String(value);

const count = Number(value);

const flag = Boolean(value);

const text = "hello";

const count = 42;

const flag = true;

Options

This rule is not configurable.

When Not To Use It

If you intentionally use object wrappers for primitives, for example to attach custom properties to a value, you may disable this rule. However, this pattern is extremely rare in modern JavaScript and TypeScript codebases.

Further Reading

• MDN documentation on String primitives and String objects
• MDN documentation on Number
• MDN documentation on Boolean

Equivalents in Other Linters

• Biome: useConsistentBuiltinInstantiation
• ESLint: no-new-wrappers
• Oxlint: eslint/no-new-wrappers