The benchmark titled "JavaScript spread operator vs object update performance 2" evaluates two different methods for updating JavaScript objects to determine which is more efficient.

Test Cases Compared

1. Using Update:

   const firstObject = {};
   firstObject.sample1 = 'Hello world';
   firstObject.sample2 = 'foo bar';
   

   This test case initializes an empty object (firstObject) and directly adds properties to it.

2. Using Object Assign:

   const firstObject = {};
   const secondObject = { ...firstObject, sample1: 'foo bar' };
   const finalObject = { ...secondObject, sample2: 'Hello world' };
   

   In this scenario, the test creates a new object (secondObject) by using the spread operator (...) to copy properties from firstObject and adds a new property (sample1). It then creates another new object (finalObject) again using the spread operator to include properties from secondObject and adds another new property (sample2).

Performance Results

The benchmark results indicate the following executions per second:

• Using Update: 119,415,592.0
• Using Object Assign: 34,574,624.0

This shows that directly updating an object is significantly faster than creating new objects using the spread operator.

Pros and Cons

Using Update:

• Pros:
  • High performance: Directly mutating an object is faster because it does not involve creating new objects or additional memory overhead.
  • Simplicity: The code is straightforward and explicit about what is happening.
• Cons:
  • Side Effects: Mutating an existing object can lead to undesired side effects, especially in functional programming paradigms where immutability is preferred.

Using Object Assign (via spread operator):

• Pros:
  • Immutability: By creating new objects rather than mutating an existing one, it helps to avoid side effects and maintains the integrity of data, making the code easier to reason about, particularly in state management (e.g., in Redux).
  • Conciseness: The spread operator provides a shorthand way to copy properties from one object to another.
• Cons:
  • Performance: Slower due to object creation, which involves additional memory allocation and garbage collection overhead.
  • Memory Usage: Creates new objects rather than modifying existing ones, which can lead to increased memory pressure in heavy use cases.

Other Considerations

• The spread operator (...) is a feature of ES6 (ECMAScript 2015) that allows for expanding iterable objects into places like function calls or array literals. In the context of objects, it allows for creating shallow copies of objects and merging properties from multiple objects.
• While Object.assign() can also be used for similar operations, the spread syntax is generally more concise and is preferred for readability in many contemporary JavaScript codebases.

Alternatives

• Object.assign(): You could use Object.assign({}, firstObject, { sample1: 'foo bar' }) for creating new object instances, though it will also typically be slower than direct object updates.
• Functional Libraries: Libraries like Immutable.js or Immer facilitate immutability with performance optimizations but come with their own learning curves and learning overhead.
• Pure Function Approach: Leveraging pure functions that do not mutate state but return new instances of objects may lead to clearer logic but at the cost of performance.

In conclusion, the benchmark shows that while using updates is more performant, it sacrifices some immutability benefits. Choosing the right approach often depends on the specific requirements of the application and the desired trade-offs between performance and immutability.