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var vs let vs const
(version: 0)
Comparing performance of:
var vs let vs const
Created:
2 years ago
by:
Guest
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Tests:
var
var g = { e: [] } g.o = function(x) { g.e.push(...[1,2,3]) } g.o()
let
let g = { e: [] } g.o = function(x) { g.e.push(...[1,2,3]) } g.o()
const
const g = { e: [] } g.o = function(x) { g.e.push(...[1,2,3]) } g.o()
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Suite status:
<idle, ready to run>
Run tests (3)
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Test case name
Result
var
let
const
Fastest:
N/A
Slowest:
N/A
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Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
Let's dive into the benchmark test cases. **What is being tested?** The provided JSON represents a benchmarking test case that compares the performance of three variable declarations in JavaScript: `var`, `let`, and `const`. Each test case creates an object `g` with an empty array `e` and defines a function `o` that pushes elements into the array using the spread operator (`...`). The test cases then execute the function `n` times, measuring the execution time. **Options being compared** The three options being compared are: 1. **`var`**: A legacy variable declaration that hoists the variable to the top of its scope. 2. **`let`**: A block-scoped variable declaration that allows re-declaration within the same scope. 3. **`const`**: A constant variable declaration that also hoists the variable, but cannot be reassigned. **Pros and Cons** 1. **`var`**: * Pros: Simple, widely supported, and easy to use in older JavaScript environments. * Cons: Hoisting can lead to unexpected behavior due to scope issues, and it's no longer recommended for new code. 2. **`let`**: * Pros: Block-scoped, allowing re-declaration within the same scope, and provides a safer alternative to `var`. * Cons: Not supported in older JavaScript environments (pre ES6). 3. **`const`**: * Pros: Provides immutability and is thread-safe. * Cons: Can be restrictive if not used carefully, as it prevents re-assignment. **Library usage** None of the test cases use any external libraries. The only library mentioned in the benchmark result is `Safari`, which indicates that the tests are being run on a mobile Safari browser. **Special JavaScript features or syntax** The test uses the spread operator (`...`) to push elements into the array, which is a feature introduced in ECMAScript 2015 (ES6). This ensures that the test results accurately reflect the performance of these variables in modern JavaScript environments. **Other alternatives** In the past, other variable declarations were used in JavaScript: * **`function`**: An older variable declaration that can only be assigned a value once. * **`var with init`**: A variation of `var` that initializes the variable at declaration time, but still has hoisting issues. However, these alternatives are no longer commonly used and have been largely replaced by `let`, `const`, and other modern features.
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