Benchmark: Objects spread vs .assign (2)

Script Preparation code:

const l = new Array(1e5).fill(null)
var objA = Object.fromEntries(l.map((i, idx) => [i + 'x', idx]))
var objB = Object.fromEntries(l.map((i, idx) => [i + 'y', idx]))

Tests:

.assign
const x = Object.assign({}, objA, objB)
spread
const x = { ...objA, ...objB }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
.assign
spread

Fastest: N/A

Slowest: N/A

Latest run results:

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Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

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**Benchmark Definition**

The benchmark measures the performance of two approaches to merge objects: `Object.assign()` and object spread syntax (`{ ...objA, ...objB }`). The script preparation code creates large arrays `l` filled with null values, which are then mapped to create objects `objA` and `objB`. These objects are used as input for the benchmark.

**Options Compared**

Two approaches are compared:

1. **Object.assign()**: This method takes multiple objects as arguments and merges them into a new object.
2. **Object spread syntax (`{ ...objA, ...objB }`)**: This syntax uses the spread operator to create a new object that includes all properties from `objA` and `objB`.

**Pros and Cons**

*   **Object.assign()**: Pros:
    *   Widely supported by most browsers.
    *   Can be used with multiple sources of truth (objects, arrays).
    Cons:
    *   Can lead to shallow copying if not properly handled.
    *   May have performance implications due to the need for a separate function call.
*   **Object spread syntax (`{ ...objA, ...objB }`)**: Pros:
    *   More modern and expressive syntax.
    *   Avoids the need for an explicit `assign()` method.
    Cons:
    *   Less widely supported by older browsers (prior to Chrome 60).
    *   May have performance implications due to the creation of a new object.

**Library**

None. The benchmark relies solely on built-in JavaScript functionality.

**Special JS Features/Syntax**

The benchmark uses modern JavaScript features, specifically:

*   **Template literals**: Used in `var objA = Object.fromEntries(l.map((i, idx) => [i + 'x', idx]))` and `var objB = Object.fromEntries(l.map((i, idx) => [i + 'y', idx]))`.
*   **Object spread syntax**: Used in the second test case (`const x = { ...objA, ...objB }`).

**Other Alternatives**

For merging objects, other approaches include:

1.  **Loose equal operator (`===`) with `null`**: Using a loose comparison to check if an object is empty or not.
    ```javascript
if (x === null || x === undefined) {
  // Handle the case where the result is null or undefined
}
```
2.  **Boolean equality operator (`==`) with `null`**: Similar to the previous approach, but uses a loose comparison for primitive values.
3.  **Using `Object.keys()` and `reduce()`**: Iterate over object keys using `keys()` and merge properties using `reduce()`.
    ```javascript
const result = Object.keys(objA).concat(Object.keys(objB))
  .reduce((acc, key) => {
    acc[key] = objA[key];
    return acc;
  }, {});
```
4.  **Using a library like Lodash**: Provides functions for merging objects, such as `_.merge()`.

Keep in mind that the choice of approach depends on your specific requirements and use cases. The benchmark provided by MeasureThat.net aims to compare the performance of two widely used methods, making it easier to choose between them based on performance characteristics.

Related benchmarks:

Objects spread vs .assign (2) (version: 1)

Comparing performance of: .assign vs spread

Created: 3 years ago by: Registered User

Jump to the latest result

.assign

spread

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):