Benchmark: const vs let vs var

Tests:

var
var g = { e: [] } g.o = function(x) { g.e.push(...[1,2,3]) } g.o()
let
var 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()

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
var
let
const

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 3 months ago)

User agent: Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/140.0.0.0 Mobile Safari/537.36

Browser/OS: Chrome Mobile 140 on Android

View result in a separate tab

Test name	Executions per second
var	6321395.5 Ops/sec
let	6483139.5 Ops/sec
const	6368289.0 Ops/sec

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

LLMs can make mistakes. Check important info.

I'll explain what's tested in the provided JSON benchmark.

The test measures the performance difference between three JavaScript variable declarations: `const`, `let`, and `var`. The script is designed to push an array of numbers onto a nested object using two different methods: assigning directly to the property (`g.e`) versus calling a function that modifies the same property (`g.o()`).

**Options compared:**

1. `const` (constant): Declares a variable that cannot be reassigned.
2. `let`: Declares a variable that can be reassigned, but not within its own block scope (i.e., inside an `if` or `loop` statement).
3. `var`: Declares a variable that can be reassigned anywhere in the function.

**Pros and cons of each approach:**

* `const`:
	+ Pros: Memory efficiency, because the variable cannot be changed, which reduces the likelihood of unintended side effects.
	+ Cons: Cannot be reassigned; if the value is needed to be modified, a new constant should be created.
* `let`:
	+ Pros: More efficient than `var`, since it redeclares the variable's scope and creates a new context.
	+ Cons: Not suitable for functions or loops where reassignment might occur.
* `var`:
	+ Pros: Can be used in any context, but it can lead to unintended side effects due to global scope.
	+ Cons: Memory inefficiency, as variables are stored on the global scope, and their values can affect other parts of the code.

**Library usage:** None

There is no external library used in this benchmark.

**Special JS features/syntax:** None mentioned

There's no special JavaScript feature or syntax being tested in this benchmark.

Now, let's discuss some alternative approaches to testing performance differences between these variable declarations:

1. **Simple loop**: Create a simple loop that assigns and reassigns values using each variable declaration.
2. **Object iteration**: Create an object with nested properties and iterate over it using each variable declaration.
3. **Array manipulation**: Create an array of numbers and use `map()`, `filter()`, or other methods to modify its contents, comparing the performance differences between `const`, `let`, and `var`.
4. **Nested function calls**: Create a nested function that modifies variables declared with each keyword.

These alternatives can provide more comprehensive insights into the performance characteristics of each variable declaration.

Related benchmarks:

const vs let vs var (version: 0)

Comparing performance of: var vs let vs const

Created: 7 years ago by: Guest

Jump to the latest result

var

let

const

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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