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detecting if var is instance of class
(version: 0)
Comparing performance of:
instanceof vs prop test
Created:
2 years ago
by:
Guest
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Tests:
instanceof
class NewError extends Error { constructor() { super() this.customProp = 'blah' } customProp } const testErr = new NewError() testErr instanceof NewError
prop test
class NewError extends Error { constructor() { super() this.customProp = 'blah' } customProp } const testErr = new NewError() !!testErr && typeof testErr === 'object' && 'customProp' in testErr
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Suite status:
<idle, ready to run>
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Test case name
Result
instanceof
prop test
Fastest:
N/A
Slowest:
N/A
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Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
**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.
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