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let vs const v5
(version: 0)
Benchmark.js
Comparing performance of:
let vs const vs func
Created:
2 years ago
by:
Guest
Go to the latest result
Script Preparation code:
const m = new Map([['key', 'value']]);
Tests:
let
let m = new Map([['key', 'value']]); let send = (agg) => {agg.get('key')}; send(m);
const
const m = new Map([['key', 'value']]); const send = (agg) => {agg.get('key')}; send(m);
func
var m = new Map([['key', 'value']]); function send(agg) {agg.get('key')} send(m);
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (3)
Previous results
Fork
Test case name
Result
let
const
func
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) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36
Browser/OS:
Chrome 118 on Linux
View result in a separate tab
Embed
Embed Benchmark Result
<iframe src="https://measurethat.net/Embed?id=508118" width="100%" height="500px"></iframe>
const
8.1M/s
func
8.1M/s
let
7.3M/s
View exact numbers
Test name
Executions per second
✓
const
8,117,548 Ops/sec
func
8,069,468 Ops/sec
let
7,282,964 Ops/sec
Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net! **Overview** The benchmark tests three ways to declare variables in JavaScript: `let`, `const`, and `var`. The goal is to compare the performance of these variables in a specific scenario. **Test Case Breakdown** Each test case represents a single variable declaration, with the corresponding function that uses the declared variable. Here's a brief explanation of each test case: 1. **`let m = new Map([['key', 'value']]);`** * This is a simple declaration using `let`, which creates a new scope for the variable. 2. **`const m = new Map([['key', 'value']]);`** * This uses the `const` keyword, which declares a constant that cannot be reassigned. The variable is still in scope, but it can't be changed. 3. **`var m = new Map([['key', 'value']]);`** * This uses the `var` keyword, which creates a global variable by default. The function's scope doesn't affect this variable. **Library and Syntax Considerations** The test cases use the `Map` API to store data, but no specific library is required for this benchmark. No special JavaScript features or syntax are used in these test cases. **Benchmark Results** The latest results show that: * **`const m = new Map([['key', 'value']]);`** performs best, with an average of 7282964.5 executions per second. * **`var m = new Map([['key', 'value']]);`** comes in second, with an average of 8069468.5 executions per second. * **`let m = new Map([['key', 'value']]);`** has the lowest performance, with an average of 8117547.5 executions per second. **Pros and Cons** Here's a brief analysis of each approach: * **`const m = new Map([['key', 'value']]);`** + Pros: No reassignment issues, clear intention for immutability. + Cons: Can't be changed after declaration. * **`var m = new Map([['key', 'value']]);`** + Pros: Global scope can be beneficial in some cases. + Cons: Default global scope, potential for naming conflicts. * **`let m = new Map([['key', 'value']]);`** + Pros: Modern syntax, allows reassignment after declaration. + Cons: May lead to confusion or unexpected behavior if not used carefully. **Alternatives** Other alternatives for declaring variables in JavaScript include: * `let`, which is similar to `const` but can be reassigned. * `var`, which creates a global variable by default (although it's generally discouraged due to potential naming conflicts and scoping issues). * Other esoteric or legacy syntax, such as `eval` or ` Function()`, which are not recommended for production code. In summary, the benchmark results suggest that using `const` for variables is generally the best approach, followed by `var` (though it's still a bit of an older pattern), and then `let`. However, the choice ultimately depends on the specific requirements and constraints of your project.
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