Benchmark: var vs let - MeasureThat.net

Tests:

let
for(let i = 0; i < 100; i++){ }
var
for(var i = 0; i < 100; i++){ }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
let
var

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 8 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.79 Safari/537.36 Edge/14.14393

Browser/OS: Chrome 51 on Windows

View result in a separate tab

Test name	Executions per second
let	212022.9 Ops/sec
var	28939314.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark JSON and explain what's being tested.

**Benchmark Definition**

The benchmark definition is a simple JavaScript script that uses a `for` loop to iterate 100 times. The only difference between the two scripts is the variable declaration:

1. `let i = 0;`
2. `var i = 0;`

This is the core of what's being tested: how different variable declarations affect performance.

**Comparison Options**

There are two main options being compared:

1. **`let`**: The "Let" option uses the `let` keyword to declare a variable, which is a block-scoped variable declaration introduced in ECMAScript 2015 (ES6).
2. **`var`**: The "Var" option uses the `var` keyword to declare a variable, which is function-scoped and has been the default variable declaration mechanism since ES5.

**Pros and Cons of Each Approach**

**`let`:**

Pros:

* Block-scoping provides better encapsulation and avoids polluting the global scope.
* Can help prevent common issues like variable hoisting and timing-related bugs.

Cons:

* May incur a small overhead due to the additional syntax.
* Requires support for ES6+ syntax, which might not be available in older browsers or environments.

**`var`:**

Pros:

* Widely supported across older browsers and environments.
* Has lower syntax overhead compared to `let`.

Cons:

* Can lead to common issues like variable hoisting, timing-related bugs, and polluting the global scope.
* May require additional code or workarounds to manage scope.

**Other Considerations**

When choosing between `let` and `var`, consider the following factors:

* Performance: In most cases, the difference is negligible. However, if you're working on a performance-critical application, using `let` might provide a slight advantage.
* Code readability and maintainability: Using `let` can make your code more readable and easier to understand, as it clearly indicates the scope of each variable.
* Browser support: If you need to support older browsers or environments, using `var` might be a better choice.

**Library Use**

In this benchmark, no libraries are used. The tests only rely on standard JavaScript features.

**Special JS Feature/ Syntax**

There is no special JS feature or syntax being tested in this benchmark. Both options use the same basic loop structure and variable declaration mechanism.

Now that we've broken down the benchmark, let's consider alternative approaches:

* **Alternative Variable Declarations**: Other variable declaration mechanisms like `const`, `let` with default values, or even global variables could be used as alternatives to compare performance.
* **Variable Hoisting**: To test the impact of variable hoisting, you could add a line of code that relies on the value of `i` before its initialization. This would highlight the issues caused by `var`'s function-scoped behavior.
* **Scoping and Encapsulation**: You could create a more complex scenario with nested loops or closures to test how different variable declarations affect scoping and encapsulation.
* **Real-World Scenarios**: To make the benchmark more realistic, you could add additional elements, such as user input or external dependencies, to simulate real-world scenarios.

Keep in mind that these alternatives would require modifications to the benchmark definition and script preparation code.

Related benchmarks:

var vs let (version: 0)

Comparing performance of: let vs var

Created: 8 years ago by: Guest

Jump to the latest result

let

var

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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