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test const vs let
(version: 0)
Comparing performance of:
const vs let
Created:
4 years ago
by:
Guest
Go to the latest result
Tests:
const
const num = 500; const nums = []; for(let i = 0; i < 100; ++i) { nums.push(String(num)); }
let
let num = 500; let nums = []; for(let i = 0; i < 100; ++i) { nums.push(String(num)); }
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (2)
Previous results
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Test case name
Result
const
let
Fastest:
N/A
Slowest:
N/A
Latest run results:
Run details:
(Test run date:
2 years ago
)
User agent:
Mozilla/5.0 (X11; Linux x86_64; rv:125.0) Gecko/20100101 Firefox/125.0
Browser/OS:
Firefox 125 on Linux
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<iframe src="https://measurethat.net/Embed?id=522282" width="100%" height="500px"></iframe>
let
5.0M/s
const
4.8M/s
View exact numbers
Test name
Executions per second
✓
let
5,014,172 Ops/sec
const
4,843,576 Ops/sec
Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
Let's dive into the world of JavaScript microbenchmarks. **What is tested?** The provided JSON represents two test cases: `const` and `let`. Both test cases measure the performance difference between using `const` and `let` variables in a JavaScript loop. Specifically, they compare how long it takes to create an array (`nums`) by pushing a string value (`String(num)`) 100 times. **Options compared** The two options being compared are: 1. **`const`**: Variables declared with the `const` keyword are "immutable" and cannot be reassigned once declared. 2. **`let`**: Variables declared with the `let` keyword are "mutable" and can be reassigned after declaration. **Pros and Cons** * **`const`**: + Pros: Since `num` is not reassignable, the loop doesn't need to check if the value has changed before updating it. This could lead to a slight performance improvement. + Cons: When `nums.push(String(num))` is called, JavaScript needs to create a new string object and push it onto the array, which might incur additional overhead due to the immutability of `const`. * **`let`**: + Pros: In each iteration of the loop, JavaScript can simply update the existing value of `num`, without creating a new string object. + Cons: Since `num` is reassignable, JavaScript needs to check if the value has changed before updating it, which might introduce additional overhead. In general, `const` can provide some performance benefits in this specific scenario due to its immutability, but the difference is likely to be small and may not be noticeable in most cases. **Library and purpose** There are no libraries mentioned in the provided JSON. The code snippets only use built-in JavaScript features. **Special JS feature or syntax** The test case uses a feature called "string coercion" in JavaScript, where `String(num)` is used to convert an integer value (`num`) to a string. This can lead to additional overhead due to the creation of new string objects. **Other alternatives** Alternative approaches could be: * Using a different data structure, like an array with a fixed size, instead of creating and pushing strings onto an array. * Using a library or framework that optimizes loop performance, such as V8's built-in optimizations for loops. * Compiling the JavaScript code to machine code using a just-in-time (JIT) compiler or ahead-of-time (AOT) compiler. Keep in mind that these alternatives would require significant changes to the test case and may not provide a meaningful comparison with the original implementation.
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