Benchmark: Plain object, for vs for in vs for of

Script Preparation code:

var a = {
    first: 'john',
    last: 'smith',
    address: {
        street: 'street street'
    }
};

var b = {
    first: 'j',
    last: 's'
};

Tests:

for loop
const props = Object.keys(a); const length = props.length; let hasNewKey = false; for (let i = 0; i < length; i++) { const key = props[i]; if (!(key in b)) { hasNewkey = true; } }
for of
const props = Object.keys(a); let hasNewKey = false; for (const key of props) { if (!(key in b)) { hasNewkey = true; } }
for in
let hasNewKey = false; for (const key in a) { if (!(key in b)) { hasNewkey = true; } }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for loop
for of
for in

Fastest: N/A

Slowest: N/A

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

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**Benchmark Explanation**

The provided benchmark compares the performance of three different approaches for iterating over an object's keys in JavaScript: `for`, `for in`, and `for of`. The test cases use a plain object `a` with multiple properties, including another nested object `address`.

**Options Compared**

1. **For Loop**: A traditional loop using the `for` keyword.
2. **For In Loop**: A loop that iterates over an object's own enumerable properties using the `in` operator.
3. **For Of Loop**: A newer loop introduced in ECMAScript 2015, which allows iterating over iterable objects (like arrays or plain objects) without using the `for` keyword.

**Pros and Cons**

* **For Loop**:
	+ Pros: Simple, widely supported, and easy to understand.
	+ Cons: May not be as efficient as other options for large datasets or when iterating over specific properties.
* **For In Loop**:
	+ Pros: Allows iteration over object keys, but can be less efficient than `for` loops due to the need to check if a property is enumerable.
	+ Cons: Can lead to unexpected behavior if not used carefully (e.g., iterating over inherited properties).
* **For Of Loop**:
	+ Pros: Efficient and concise way to iterate over iterable objects, making it suitable for large datasets or complex object structures.
	+ Cons: Requires ECMAScript 2015 support, which may limit its applicability.

**Library/ Syntax Considerations**

None of the test cases use a specific library. However, the `for in` loop option might be affected by the presence of inherited properties if the object has prototype chains.

**Special JS Feature/Syntax**

The `For Of Loop` option uses a new JavaScript feature introduced in ECMAScript 2015, allowing iteration over iterable objects without using the `for` keyword. This syntax is relatively modern and might not be supported by older browsers or versions of JavaScript.

**Other Alternatives**

In addition to the mentioned options, other approaches for iterating over object keys include:

1. Using the `Object.keys()` method (as shown in one of the test cases).
2. Utilizing a library like Lodash's `keys()` function.
3. Implementing a custom iteration mechanism using `forEach` and checking if each property is present in the target object.

Keep in mind that these alternatives might offer different trade-offs in terms of performance, readability, or compatibility with older browsers.

Related benchmarks:

Plain object, for vs for in vs for of (version: 0)

Comparing performance of: for loop vs for of vs for in

Created: 3 years ago by: Guest

Jump to the latest result

for loop

for of

for in

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):