Overview of the Benchmark

The provided benchmark is designed to measure the performance of JavaScript engines in detecting whether a variable var is an instance of a class. The test cases are simple, yet revealing of how different JavaScript engines approach type checking and object property access.

Benchmark Definition

The benchmark definition represents a script that defines a custom error class NewError with a custom property customProp. A new instance of the NewError class is created and used to create two test cases:

1. instanceof: Verifies whether the instance of NewError is itself an instance of the NewError class using the instanceof operator.
2. prop test: Checks if the instance has a property named customProp using the in operator and checks if it's a string.

Options Compared

The two options being compared are:

1. Using the instanceof operator to check for class inheritance
2. Using the in operator to access object properties

Pros and Cons of Each Approach

instanceof

• Pros: Efficient, straightforward, and easy to understand.
  • The instanceof operator is a built-in operator that checks if an instance is an instance of a specific constructor function or class.
  • It's often preferred for its readability and maintainability.
• Cons:
  • May be slower than the alternative approach due to additional checks performed by the engine.
  • Does not provide information about whether the property exists but is null.

in

• Pros: More general-purpose, as it can also check if a property exists in an object even if its value is null or undefined.
  • Can be more efficient than instanceof for certain scenarios.
• Cons:
  • Less readable and maintainable due to the implicit nature of the operation.
  • May require additional checks to ensure accuracy.

Library Used

None, as this benchmark does not rely on any external libraries. The test code is self-contained within the JSON definitions.

Special JS Feature or Syntax

The instanceof operator and the in operator are built-in JavaScript operators that do not require special knowledge of features or syntax beyond basic JavaScript syntax.

Other Alternatives

In general, other alternatives to these approaches might involve:

• Using a more advanced type checking library (e.g., TypeScript) for class-based inheritance detection.
• Employing runtime checks using assert() or similar functions to verify the presence and value of specific properties in objects.
• Utilizing engine-specific optimizations (if applicable) like those provided by certain JavaScript engines.

Keep in mind that these alternatives may have varying levels of feasibility, complexity, and performance impact compared to the original benchmark options.