Benchmark: guarded for-in vs object.keys

Script Preparation code:

var obj = {
  'a': 1,
  'b': 1,
  'c': 1,
  'd': 1,
  'e': 1,
  'f': 1,
  'g': 1
};

Tests:

for-in
for (var i=10000; i > 0; i--) { for (var key in obj) { if(Object.prototype.hasOwnProperty.call(obj, key)){ console.log(key); } } }
Object.keys
for (var i=10000; i > 0; i--) { Object.keys(obj).forEach(key => console.log(key)); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for-in
Object.keys

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 provided benchmark is comparing two approaches to iterate over an object: `for-in` and `Object.keys`.

**Options Compared**

*   `for-in`: This approach uses a traditional `for` loop with an index variable (`i`) to iterate over the object's properties. The iteration checks if each property belongs to the object using `Object.prototype.hasOwnProperty.call()`.
*   `Object.keys`: This approach utilizes the `Object.keys()` method, which returns an array of a given object's own enumerable property names.

**Pros and Cons**

*   **for-in**: 
    *   Pros: 
        *   Can be more straightforward for iterating over objects that don't follow the standard naming conventions.
        *   Less overhead since it doesn't require additional memory allocation.
    *   Cons:
        *   More complex due to the index variable and additional checks.
        *   May have a performance hit if the object is large or has many properties.
*   `Object.keys`:
    *   Pros: 
        *   Slicker syntax that directly accesses an array of property names.
        *   Typically faster since it leverages the built-in method to access these values.
    *   Cons:
        *   Can be slower due to memory allocation and garbage collection overhead.
        *   May not work as expected if you try to modify properties during iteration.

**Library and Purpose**

In this benchmark, `Object.keys()` is a built-in JavaScript library (specifically an object method) that provides a convenient way to get the array of property names for an object. This allows users to easily compare its performance against other methods.

**Special JS Features or Syntax**

The provided benchmark does not explicitly mention any special JavaScript features or syntax, except for `Object.prototype.hasOwnProperty.call()`, which is used in the `for-in` approach. However, it's worth noting that this method can be replaced with a more efficient and idiomatic way using the bracket notation (`[key] in obj`) if available (although some older browsers may not support it).

**Other Alternatives**

In general, there are other methods to iterate over objects in JavaScript:

*   **forEach()**: This is another built-in array method that can be used with objects.
    ```javascript
for (var key in obj) {
  obj[key].forEach(function(value) {
    console.log(key + ": " + value);
  });
}
```

*   **for...in**: While this method has been criticized for its performance, some users might prefer it due to its straightforward nature.

*   **Array.from() and spread operator (`...`)**: 
    ```javascript
const keys = Object.keys(obj);
for (var key of keys) {
  console.log(key);
}
```

Please note that while `Object.keys()` is often the preferred method, other methods have their own advantages.

Related benchmarks:

guarded for-in vs object.keys (version: 0)

Comparing performance of: for-in vs Object.keys

Created: 5 years ago by: Guest

Jump to the latest result

for-in

Object.keys

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):