What causes " : No property name supplied Usage: spyOn( , )" in jestjs/jest?

Pass the literal property name: spyOn(obj, 'value', 'get').

jestjs/jest · error · Error

<spyOn> : No property name supplied Usage: spyOn(<object>, <

Error message

<spyOn> : No property name supplied
Usage: spyOn(<object>, <methodName>)

What it means

Thrown by SpyRegistry._spyOnProperty when propertyName is falsy (spyRegistry.ts:162-164). The property name selects which accessor descriptor to replace; without it the registry cannot locate the getter/setter to spy on.

Source

Thrown at packages/jest-jasmine2/src/jasmine/spyRegistry.ts:163

        restoreObjectToOriginalState: restoreStrategy,
      } as Spy);

      obj[methodName] = spiedMethod;

      return spiedMethod;
    };

    this._spyOnProperty = function (obj, propertyName, accessType = 'get') {
      if (!obj) {
        throw new Error(
          getErrorMsg(
            `could not find an object to spy upon for ${propertyName}`,
          ),
        );
      }

      if (!propertyName) {
        throw new Error(getErrorMsg('No property name supplied'));
      }

      let descriptor: PropertyDescriptor | undefined;
      try {
        descriptor = Object.getOwnPropertyDescriptor(obj, propertyName);
      } catch {
        // IE 8 doesn't support `definePropery` on non-DOM nodes
      }

      if (!descriptor) {
        throw new Error(getErrorMsg(`${propertyName} property does not exist`));
      }

      if (!descriptor.configurable) {
        throw new Error(
          getErrorMsg(`${propertyName} is not declared configurable`),
        );
      }

View on GitHub (pinned to 8e6d128e4a)

Solutions

Pass the literal property name: spyOn(obj, 'value', 'get').
If dynamic, validate first: if (!name) throw new Error('property name required'); spyOn(obj, name, 'get').
Type propertyName as keyof typeof obj to catch undefined at compile time.
Review auto-formatter output that may have dropped a line.

Example fix

// before
spyOn(obj, undefined, 'get');
// after
spyOn(obj, 'value', 'get');

Defensive patterns

Strategy: validation

Validate before calling

if (!propertyName) {
  throw new Error('spyOn property: propertyName is required');
}
spyOn(obj, propertyName, 'get');

Type guard

const isPropertyName = (v: unknown): v is string =>
  typeof v === 'string' && v.length > 0;

Prevention

Pass a non-empty property name string.
Type propertyName as keyof typeof obj.
Review formatter output after refactors.

When it happens

Trigger: spyOn(obj, undefined, 'get'), spyOn(obj, '', 'get'), spyOn(obj) with the accessType arg pushed out, or a dynamically-computed name that resolved to an empty string.

Common situations: Refactor that renamed the property but left the spy on the old name variable computed elsewhere; destructuring that lost the name; copy-paste of a spy template that omitted the second arg.

Related errors

AI-assisted analysis of jestjs/jest@8e6d128e4a (2026-08-10). Data as JSON: /api/errors/6e12a6b48fe84d43. Report an issue: GitHub.