Benchmark: GlobalVariable vs getElementById

HTML Preparation code:

<table id="tasks-table">
</table>

Script Preparation code:

let table = document.getElementById('tasks-table');
for(let i=0; i<5000; i++)
{
  let tr = document.createElement('tr');
  tr.classList.add('task-row')
  table.append(tr);
}

Tests:

Global Variable
let table = document.getElementById('tasks-table'); for(var i=0; i<5000; i++) { let row = table.children[i]; row.innerText = "Blabla"; }
getElementByid
for(var i=0; i<5000; i++) { let row = document.getElementById('tasks-table').children[i]; row.innerText = "Blabla"; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Global Variable
getElementByid

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):

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Let's break down the benchmark and explain what's being tested, compared, and the pros/cons of each approach.

**Benchmark Purpose**

The benchmark measures the performance difference between two approaches: using a global variable (`let table = ...`) versus using `getElementById` to access an element in a table. The test case creates a table with 5000 rows, appends a new row for each iteration, and updates the text content of each row.

**Approaches Compared**

There are two approaches compared:

1. **Global Variable**: Using a global variable (`let table = ...`) to store the reference to the table element. In each iteration, it accesses `table.children[i]` to get the nth row.
2. **getElementById**: Using `document.getElementById('tasks-table')` to access the table element by its ID. In each iteration, it accesses the children array of the table element using `children[i]`.

**Pros and Cons**

**Global Variable Approach**

Pros:

* More concise and readable code
* No need to look up the table element's ID every time

Cons:

* May lead to slower performance if the table is very large or dynamically generated, as it involves accessing the children array of the global variable.
* May not work well in environments where the global variable is not accessible (e.g., in a worker thread).

**getElementById Approach**

Pros:

* Direct access to the element's children array without any additional lookup
* Works well even when the table is very large or dynamically generated

Cons:

* Requires an extra step to look up the element's ID every time
* May be less readable and more verbose

**Other Considerations**

* The benchmark uses `for...of` loop instead of traditional `for` loop with `var i`. This is a good practice as it avoids polluting the global scope and makes the code more concise.
* The test case creates a new row for each iteration, which can lead to increased memory allocation and garbage collection. This may impact performance in certain scenarios.

**Library Used**

None explicitly mentioned in the benchmark definition.

**Special JS Feature or Syntax**

None mentioned in this particular benchmark.

However, it's worth noting that the use of `let` instead of `var` is a more modern way of declaring variables in JavaScript. The use of `for...of` loop is also a good practice for readability and performance.

**Alternatives**

Other alternatives to measure the performance difference between accessing an element by its ID or using a global variable could include:

* Using a different DOM manipulation approach, such as using CSS classes or attribute selectors.
* Measuring the performance of rendering a table with dynamic data instead of creating it in the browser's DOM.
* Using a testing library like Jest or Mocha to write and run the benchmark tests.

Related benchmarks:

GlobalVariable vs getElementById (version: 0)

Comparing performance of: Global Variable vs getElementByid

Created: 6 years ago by: Guest

Jump to the latest result

Global Variable

getElementByid

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):