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Getting last element of array
(version: 0)
Comparing performance of:
slice vs length
Created:
2 years ago
by:
Guest
Go to the latest result
Script Preparation code:
var arr = []; for (let i = 0; i < 1000000; i++) { arr.push(i); }
Tests:
slice
for (let i = 0; i < 1000; i++) { const v = arr.slice(-1)[0]; }
length
let len = arr.length - 1 for (let i = 0; i < 1000; i++) { const v = arr[len]; }
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (2)
Previous results
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Test case name
Result
slice
length
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=614246" width="100%" height="500px"></iframe>
length
3.0M/s
slice
77K/s
View exact numbers
Test name
Executions per second
✓
length
2,954,541 Ops/sec
slice
77,439 Ops/sec
Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
Let's break down the provided JSON and explain what's being tested, compared options, pros and cons, and other considerations. **Benchmark Definition** The benchmark is testing two approaches to get the last element of an array: using `slice()` method or accessing the array length directly (`length` property). **Script Preparation Code** The script preparation code creates a large array with 1 million elements and assigns it to the variable `arr`. This ensures that both test cases operate on a large enough dataset. **Html Preparation Code** There is no HTML preparation code provided, which means that only the JavaScript aspect of the benchmark is being tested. **Options Compared** 1. **Using slice() method**: The first test case uses the `slice()` method to get the last element of the array. Specifically, it calls `arr.slice(-1)[0]`. 2. **Accessing length directly**: The second test case accesses the array length directly using `len = arr.length - 1` and then uses this value to get the last element. **Pros and Cons** * **Using slice() method**: + Pros: Generally considered more reliable and efficient, as it handles cases where the array is modified. + Cons: May be slower for very large arrays due to its overhead. * **Accessing length directly**: + Pros: Can be faster for very large arrays, as it doesn't involve creating a new slice object. + Cons: May not handle cases where the array is modified. **Other Considerations** * The benchmark uses a relatively small dataset (1 million elements) to test both approaches. For very large datasets, the performance difference between these two methods might be negligible. * It's worth noting that in modern JavaScript engines, the `slice()` method has become more efficient due to optimizations like tail call optimization. **Library Used** None mentioned explicitly in the provided JSON. However, if we assume that the benchmark is using a standard JavaScript implementation (e.g., V8), then no additional libraries are required. **Special JS Feature/Syntax** There doesn't seem to be any special JavaScript features or syntax used in this benchmark. **Alternatives** Other approaches to get the last element of an array include: 1. `arr[arr.length - 1]`: Similar to accessing length directly, but using the property access syntax. 2. `Math.max.apply(null, arr)`: Using the `max` function and applying it to the array with `null` as the initial value. 3. `Array.prototype.at()`: A newer ES6 method (available in modern browsers and Node.js) that returns the element at a given index. These alternatives might offer different performance characteristics or trade-offs, but they are not explicitly tested in this benchmark. The provided benchmark is a simple yet informative test case for comparing the performance of two common approaches to get the last element of an array.
Related benchmarks
arr unshift vs push + reverse (large array)
`array.slice(-1)[0]` vs `array[array.length - 1]`
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