Benchmark: const vs var vs let performance in loop

Tests:

Var
var tmp; for(var i = 0;i < 250000;i++) { tmp = i * (i - 1) * (i + 1); }
Const
for(var i = 0;i < 250000;i++) { const tmp = i * (i - 1) * (i + 1); }
Let
let tmp; for(var i = 0;i < 250000;i++) { tmp = i * (i - 1) * (i + 1); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Var
Const
Let

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36

Browser/OS: Chrome 130 on Windows

View result in a separate tab

Test name	Executions per second
Var	15827.1 Ops/sec
Const	17041.2 Ops/sec
Let	16737.9 Ops/sec

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

LLMs can make mistakes. Check important info.

I'll break down the benchmark and explain what's being tested.

**Benchmark Overview**

The benchmark measures the performance difference between three different variable declaration methods: `const`, `var`, and `let`. The test case uses a loop that performs a calculation on a temporary variable `tmp`.

**Variable Declaration Methods Compared**

1. **`const`**: In this approach, the variable `tmp` is declared as `const`, which means its value cannot be changed once it's assigned.
2. **`var`**: Here, the variable `tmp` is declared with the traditional `var` keyword, allowing its value to be modified within the scope of the loop.
3. **`let`**: In this case, `tmp` is declared using the `let` keyword, which also allows its value to be changed.

**Pros and Cons of Each Approach**

* **`const`**:
	+ Pros: The variable's value is not modified, reducing unnecessary reassignments and potential memory allocations.
	+ Cons: Once initialized, the value cannot be changed, which might affect performance if the initial value needs to be recalculated or updated elsewhere in the code.
* **`var`**:
	+ Pros: Allows for easy modification of the variable's value within the scope of the loop.
	+ Cons: Reassignments can lead to unnecessary memory allocations and potential performance issues due to repeated rebindings of the variable.
* **`let`**:
	+ Pros: Provides a balance between `const` and `var`, allowing for one-time initialization and subsequent changes.
	+ Cons: Similar to `var`, reassignments can still lead to performance issues.

**Library Usage**

There is no explicit library usage in this benchmark. However, it's worth noting that the `let` and `const` declarations are part of the ECMAScript 2015 (ES6) language standard, which was adopted by most modern JavaScript engines, including those used by Chrome.

**Special JS Features or Syntax**

There is no special JavaScript feature or syntax being tested in this benchmark. The focus is on comparing the performance differences between three variable declaration methods.

**Alternatives**

If you're interested in exploring alternative approaches, consider the following:

1. **`let` with `immediate invoked function expression (IIFE)`**: Instead of declaring `tmp` as `let`, use an IIFE to initialize and assign its value immediately.
```javascript
const tmp = (i * (i - 1) * (i + 1));
for (var i = 0; i < 250000; i++) { }
```
This approach avoids reassignments and potential performance issues.

2. **`eval()`**: Use `eval()` to calculate the initial value of `tmp` and assign it directly.
```javascript
for (var i = 0; i < 250000; i++) {
  eval("const tmp = " + (i * (i - 1) * (i + 1)));
}
```
However, keep in mind that using `eval()` can lead to security vulnerabilities and performance issues due to the overhead of dynamic evaluation.

These alternative approaches are worth considering for more complex scenarios or when you need more control over variable initialization.

Related benchmarks:

const vs var vs let performance in loop (version: 0)

const vs var vs let performance in loop

Comparing performance of: Var vs Const vs Let

Created: 3 years ago by: Guest

Jump to the latest result

Var

Const

Let

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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