veve / spyOn

Function: spyOn()

spyOn<T, K>(obj, method): TrackedFunction<MethodType<T, K>>

Replaces a method on an object with a tracked version while preserving its original type signature. The original method is replaced with a tracked version that maintains the same behavior but provides additional tracking capabilities. The tracked version is both assigned to the object and returned for convenience.

Type Parameters

• T extends object

The type of the object containing the method to track

• K extends string | number | symbol

The key type of the method to track, must be a key of T

Parameters

obj

T

The object containing the method to track

method

K & MethodNames<T>

The name of the method to track

Returns

TrackedFunction<MethodType<T, K>>

A tracked version of the specified method

Throws

If the specified method doesn't exist on the object or isn't a function

Example

// Track a method on a simple object
const calculator = {
  add: (a: number, b: number) => a + b
};
const trackedAdd = spyOn(calculator, 'add');
calculator.add(2, 3); // Returns 5
console.log(trackedAdd.getCallCount()); // Returns 1

spyOn Function