Benchmark: JavaScript Object.assign vs for in loop vs for of loop

Tests:

Object.assign
const a = { x: 'xxx', y: 1, z: null } const b = { z: 1, u: 'uuu', v: null } Object.assign(a, b);
for in loop
const a = { x: 'xxx', y: 1, z: null } const b = { z: 1, u: 'uuu', v: null } for (let prop in b) a[prop] = b[prop];
for of loop
const a = { x: 'xxx', y: 1, z: null } const b = { z: 1, u: 'uuu', v: null } for (let [k,v] of Object.entries(b)) a[k] = b[v];

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Object.assign
for in loop
for of loop

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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Let's break down the benchmark and explain what's being tested.

**Benchmark Definition**

The benchmark is comparing three approaches to merge two objects in JavaScript:

1. `Object.assign()`
2. `for in loop` (using the legacy `in` operator)
3. `for...of loop` (newer iteration syntax)

These approaches aim to determine which one is the most efficient.

**Options Compared**

The options being compared are:

* **Object.assign()**: a built-in method for merging objects.
* **For in loop**: an older way of iterating over object properties using the `in` operator.
* **For...of loop**: a newer iteration syntax introduced in ECMAScript 2015 (ES6).

**Pros and Cons**

Here's a brief overview of each approach:

* **Object.assign()**:
	+ Pros: concise, efficient, and widely supported.
	+ Cons: might not work as expected with certain data types or edge cases.
* **For in loop**:
	+ Pros: can handle complex object iterations and is compatible with older browsers.
	+ Cons: less readable and less efficient compared to newer syntaxes.
* **For...of loop**:
	+ Pros: more modern, concise, and efficient (although still relatively new).
	+ Cons: might not be supported in older browsers or require additional imports.

**Library**

In this benchmark, there is no explicit library being used. The three methods are native JavaScript constructs.

**Special JS Feature/Syntax**

The `for...of loop` syntax introduced in ES6 is a newer feature that allows iterating over iterable objects (such as arrays and objects) using the `for...of` statement.

**Benchmark Results**

According to the latest benchmark results, the order of execution performance for the three methods is:

1. `for in loop`: 47,770,011 executions per second
2. `Object.assign()`: 4,783,011 executions per second
3. `for...of loop`: 29,737,222 executions per second

These results suggest that the `for...of loop` is the most efficient approach among the three.

**Other Alternatives**

If you were to explore alternative approaches, some options might include:

* Using a library like Lodash or Ramda for object merging.
* Utilizing ES7+ features like optional chaining (`?.`) and template literals (``) for more concise code.
* Employing other iteration methods, such as `forEach()` or array destructuring.

However, these alternatives might not necessarily outperform the native JavaScript approaches in terms of performance.

Related benchmarks:

JavaScript Object.assign vs for in loop vs for of loop (version: 0)

Comparing performance of: Object.assign vs for in loop vs for of loop

Created: 4 years ago by: Guest

Jump to the latest result

Object.assign

for in loop

for of loop

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):