Benchmark: For in vs Object.keys.forEach vs For of Object.keys

Script Preparation code:

var obj = new Object()
var keys = (new Array(100)).fill(0).map((x, i) => {
    return i + 1
})
keys.forEach((x) => {
    obj['prop' + x] = x
})

Tests:

for in
for (var key in obj) { if (obj.hasOwnProperty(key)) console.log(obj[key]) }
for each
Object.keys(obj).forEach(key => console.log(obj[key]))
for of
for (const key of Object.keys(obj)) { console.log(obj[key]) }
for of (outside const)
const keys = Object.keys(obj) for (const key of keys) { console.log(obj[key]) }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
for in
for each
for of
for of (outside const)

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

LLMs can make mistakes. Check important info.

Let's break down the provided JSON and explain what is being tested.

**Benchmark Definition**

The benchmark definition represents different approaches to iterate over an object's properties using `for` loops. There are four variations:

1. **For in**: This method uses the `in` operator to iterate over the object's property names.
2. **For each (Object.keys)**: This method uses the `Object.keys()` function to get an array of property names, and then iterates over it using `forEach`.
3. **For of (with const)**: This method uses the `for...of` loop syntax with a `const` declaration to iterate over an array of property names obtained from `Object.keys()`.
4. **For of (without const)**: This method is similar to the previous one, but the variable declaration (`const key`) is outside the `for` loop.

**Options Compared**

The four options are compared in terms of execution speed. The benchmark measures how many executions per second each option can handle.

**Pros and Cons**

Here's a brief summary of each approach:

1. **For in**: This method has the lowest overhead, as it only requires checking if the property exists on the object using `hasOwnProperty()`. However, it can be slower than other methods because it uses a more complex iteration mechanism.
2. **For each (Object.keys)**: This method is generally faster than `for in` because it uses an array-based iteration mechanism, which is optimized for performance. However, it requires an additional function call to get the property names.
3. **For of (with const)**: This method is similar to `for...of`, but with a twist. The variable declaration (`const key`) must be outside the loop, which can make it less readable. It's generally faster than `for in` because it uses a more efficient iteration mechanism.
4. **For of (without const)**: This method is identical to the previous one, except for the variable declaration location. Its performance characteristics are similar to `for...of`.

**Library and Special JS Features**

None of these options use any external libraries. However, they do employ some specific JavaScript features:

1. **Object.keys()**: This function returns an array of property names on an object.
2. **For...of loop syntax (const)**: This is a modern JavaScript feature that allows iterating over arrays or other iterable objects using the `for...of` loop syntax.

**Other Alternatives**

Some alternative approaches to iterate over an object's properties include:

1. **Using Array.prototype.forEach()**: You can use the `forEach()` method on an array of property names to iterate over them.
2. **Using a custom iterator**: If you need more control over the iteration process, you can create a custom iterator using the `Symbol.iterator` property.

Keep in mind that these alternative approaches may have different performance characteristics than the ones being compared in this benchmark.

Related benchmarks:

For in vs Object.keys.forEach vs For of Object.keys (version: 0)

Comparing performance of: for in vs for each vs for of vs for of (outside const)

Created: 4 years ago by: Guest

Jump to the latest result

for in

for each

for of

for of (outside const)

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):