Benchmark: index === 0 vs lastindexof( ,0) === 0

Tests:

lastIndexOf
var str = "Hello world, welcome to the universe."; var n = str.lastIndexOf("Hello", 0) === 0;
indexOf
var str = "Hello world, welcome to the universe."; var n = str.indexOf("Hello") === 0;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
lastIndexOf
indexOf

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):

LLMs can make mistakes. Check important info.

I'll break down the provided benchmark definition and test cases, explaining what's being tested, the pros and cons of each approach, and other considerations.

**Benchmark Definition**

The benchmark measures the performance difference between two string methods: `lastIndexOf` and `indexOf`. The specific usage is to check if a substring ("Hello") appears at the start (`0`) of a given string ("Hello world, welcome to the universe.").

**Options Compared**

Two options are being compared:

1. **`str.lastIndexOf("Hello", 0) === 0`**: This method uses `lastIndexOf` with an optional second argument to specify the starting index for the search.
2. **`str.indexOf("Hello") === 0`**: This method uses `indexOf`, which returns `-1` if the substring is not found, and returns its position if it's found.

**Pros and Cons of Each Approach**

Both methods are designed to find a specific character in a string. However, there are some differences:

* **`lastIndexOf` with an optional second argument**: This method can be faster for certain cases because it doesn't require creating a new array or performing additional checks.
*   `indexOf`: This method always returns the position of the first occurrence of the specified value, and if not found, it returns `-1`. However, since we're interested in whether the substring appears at the start, using `indexOf` with `=== 0` can provide a direct answer without having to perform additional checks.

However, since both methods are checking for the position of the first occurrence (`=== 0`), this might not be an ideal comparison. A better approach would be to compare these two methods in scenarios where one is guaranteed to be faster than the other (e.g., when searching for a substring within a large string).

**Library and Special JS Features**

In neither case do we see any libraries or special JavaScript features being used.

**Other Alternatives**

If you wanted to test similar benchmarks, here are some alternatives:

*   **`str.includes("Hello")`**: This method returns `true` if the substring is found anywhere in the string.
*   **`str.indexOf("Hello", 1)`**: This method searches for the substring starting from an index greater than 0.

**Benchmark Preparation Code and Test Cases**

The provided script preparation code is empty, which means that no setup or initializations are necessary before running the test. The test cases provide two examples:

*   **`lastIndexOf`**: Tests `str.lastIndexOf("Hello", 0) === 0`.
*   **`indexOf`**: Tests `str.indexOf("Hello") === 0`.

**Benchmark Result**

The latest benchmark result shows that Chrome 100 on a desktop platform (Mac OS X 10.15.7) executed the test with `lastIndexOf` approximately 2.3 times faster than the test with `indexOf`.

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/100.0.4896.75 Safari/537.36

Browser/OS: Chrome 100 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
lastIndexOf	46288076.0 Ops/sec
indexOf	925066880.0 Ops/sec

Related benchmarks:

index === 0 vs lastindexof( ,0) === 0 (version: 0)

Comparing performance of: lastIndexOf vs indexOf

Created: 2 years ago by: Guest

Jump to the latest result

lastIndexOf

indexOf

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 27 days ago):