Benchmark: this vs var - MeasureThat.net

Script Preparation code:

var obj = {a: {b: 0}};

Tests:

this
for(var i = 0; i < 1000; i++){ obj.a.b = i; }
var
var a = obj.a; for(var i = 0; i < 1000; i++){ a.b = i; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
this
var

Fastest: N/A

Slowest: N/A

Latest run results:

No previous run results

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

LLMs can make mistakes. Check important info.

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

**What is being tested?**

The provided JSON represents two test cases, each measuring the performance of a different approach to accessing an object property: `this` vs `var`. The script preparation code for each test case creates an object `obj` with a nested property `a.b`.

**Options compared:**

There are two approaches being compared:

1. **`this`**: This approach uses the implicit binding of the `this` keyword to access the `b` property of the `obj` object.
2. **`var`**: This approach uses a declared variable `a` to access the `b` property of the `obj` object.

**Pros and Cons:**

*   **`this`**:
    *   Pros:
        +   Easier to read and understand, as it doesn't require explicit declaration of variables.
        +   Less chance of scope-related issues due to hoisting in JavaScript.
    *   Cons:
        +   Can lead to unexpected behavior if the `obj` variable is reassigned or goes out of scope before accessing its property.
*   **`var`**:
    +   Pros:
        -   More explicit control over variable scoping and lifetime, which can be beneficial in certain situations.
        -   May perform slightly better due to less overhead from implicit binding.

However, there's a subtle but significant difference between the two approaches. In JavaScript, when using `this`, the value of `obj` is looked up along the call stack. If `obj` is reassigned or goes out of scope before accessing its property, it can lead to unexpected behavior. On the other hand, when using a declared variable like `var a`, it's not looking up a new `a` on each iteration; instead, it's always referring to the same newly-declared variable and assigning to that one.

Despite their similarities, both approaches have their trade-offs in terms of performance and readability. However, in many cases, these differences are negligible, and the choice between them comes down to coding style or specific requirements.

**Library usage:**

There is no explicit library mentioned in the provided benchmark JSON.

However, if you consider external libraries that might be used when running benchmarks on JavaScript code, we can think of a few possible candidates. One example would be a benchmarking framework like Benchmark.js. These frameworks provide ways to write high-performance benchmarks with clean, readable syntax and allow for better control over test configurations.

**Special JS feature or syntax:**

The provided JSON does not explicitly mention any special JavaScript features or syntaxes that require specific handling during benchmarking.

Related benchmarks:

this vs var (version: 0)

Comparing performance of: this vs var

Created: 5 years ago by: Guest

Jump to the latest result

this

var

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

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