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for..in vs for loop using Object.keys
(version: 0)
Benchmark.js
Comparing performance of:
for in vs for loop with object keys
Created:
5 years ago
by:
Guest
Go to the latest result
Script Preparation code:
var obj = { 'a': 1, 'b': 1, 'c': 1, 'd': 1, 'e': 1, 'f': 1, 'g': 1, 'h': 1, 'i': 1, 'j': 1, 'k': 1, 'l': 1, 'm': 1, 'n': 1, 'o': 1, 'p': 1, 'q': 1, 'r': 1, 's': 1, 't': 1, 'u': 1, 'v': 1, 'w': 1, 'x': 1, 'y': 1, 'z': 1, 'aa': 1, 'ba': 1, 'ca': 1, 'da': 1, 'ea': 1, 'fa': 1, 'ga': 1, 'ha': 1, 'ia': 1, 'ja': 1, 'ka': 1, 'la': 1, 'ma': 1, 'na': 1, 'oa': 1, 'pa': 1, 'qa': 1, 'ra': 1, 'sa': 1, 'ta': 1, 'ua': 1, 'va': 1, 'wa': 1, 'xa': 1, 'ya': 1, 'za': 1, 'ab': 1, 'bb': 1, 'cb': 1, 'db': 1, 'eb': 1, 'fb': 1, 'gb': 1, 'hb': 1, 'ib': 1, 'jb': 1, 'kb': 1, 'lb': 1, 'mb': 1, 'nb': 1, 'ob': 1, 'pb': 1, 'qb': 1, 'rb': 1, 'sb': 1, 'tb': 1, 'ub': 1, 'vb': 1, 'wb': 1, 'xb': 1, 'yb': 1, 'zb': 1 };
Tests:
for in
for (let i = 1000; i > 0; i--) { for (const key in obj) { console.log(key); } }
for loop with object keys
const keys = Object.keys(obj); for (let i = 1000; i > 0; i--) { for (let j = 0; j < keys.length; j ++) { console.log(keys[j]); } }
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (2)
Previous results
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Test case name
Result
for in
for loop with object keys
Fastest:
N/A
Slowest:
N/A
Latest run results:
Run details:
(Test run date:
one year ago
)
User agent:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/18.3 Safari/605.1.15
Browser/OS:
Safari 18 on Mac OS X 10.15.7
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Embed Benchmark Result
<iframe src="https://measurethat.net/Embed?id=583383" width="100%" height="500px"></iframe>
for loop with object keys
24/s
for in
24/s
View exact numbers
Test name
Executions per second
✓
for loop with object keys
24 Ops/sec
for in
24 Ops/sec
Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
I'll break down the provided JSON and explain what's being tested, compared options, pros and cons of each approach, and other considerations. **Benchmark Definition** The benchmark is defined by the two test cases: 1. `for in` 2. `for loop with object keys` (using `Object.keys(obj)`) Both test cases aim to iterate over a large object (`obj`) using a `for` loop. The difference lies in the way the object is iterated: * `for in`: uses the `in` operator to iterate over the object's properties. * `for loop with object keys`: uses the `Object.keys(obj)` method to get an array of the object's property names and then iterates over that array using a traditional `for` loop. **Options Compared** The two test cases compare the performance of: 1. **`for in`**: a legacy, object-specific iteration mechanism. 2. **`for loop with object keys`**: a more modern, JavaScript-agnostic approach using `Object.keys(obj)`. **Pros and Cons** **`for in`:** Pros: * Widely supported across browsers and platforms. * Simple to implement. Cons: * Not designed for iteration over arrays or other non-object types. * Can be slower due to the overhead of property iteration. * May not work as expected when dealing with objects that have missing or duplicate properties. **`for loop with object keys`:** Pros: * More efficient and modern way of iterating over objects. * Works correctly even if the object has missing or duplicate properties. * Less prone to browser quirks. Cons: * Requires the `Object.keys()` method, which may not be supported in older browsers or environments. * May require additional setup for array iteration. **Other Considerations** * The `for in` approach is often considered legacy because it's not designed specifically for iteration. It's better suited for accessing object properties dynamically using bracket notation (e.g., `obj['prop']`). * Using `Object.keys()` can lead to performance issues if the resulting array is too large, as JavaScript has to create a new array and iterate over it. * The choice between `for in` and `for loop with object keys` ultimately depends on the specific requirements of your use case. If you need to support older browsers or environments, `for in` might be necessary. **Alternative Approaches** If performance is critical and you're using a modern JavaScript engine, consider using: 1. **`Array.prototype.forEach()`**: for iterating over arrays. 2. **`Array.prototype.entries()`**: for iterating over arrays while preserving the original key-value pairs. 3. **`Object.values()`** or **`Object.entries()`**: for iterating over object values or key-value pairs, respectively. Keep in mind that these alternatives might not be suitable for every use case and may require additional setup or modifications to your existing code.
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