Benchmark: startsWith vs indexOf vs endsWith

Script Preparation code:

var start = 'hello!';
var end = 'string!';
var string = start + ' im a ' + end;

Tests:

startsWith
string.startsWith(start);
indexOf(start)
string.indexOf(start) == 0;
endsWith
string.endsWith(end);
indexOf(end)
string.indexOf(end) == (string.length - end.length);

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
startsWith
indexOf(start)
endsWith
indexOf(end)

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 5 months ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/142.0.0.0 Safari/537.36

Browser/OS: Chrome 142 on Windows

View result in a separate tab

Test name	Executions per second
startsWith	46263836.0 Ops/sec
indexOf(start)	98543680.0 Ops/sec
endsWith	37383256.0 Ops/sec
indexOf(end)	103139416.0 Ops/sec

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

LLMs can make mistakes. Check important info.

**Benchmark Overview**

The MeasureThat.net website provides a platform for users to create and run JavaScript microbenchmarks. In this case, we have a benchmark that compares the performance of three different methods to check if a string starts with a certain substring: `startsWith`, `indexOf` (with and without equality), and `endsWith`.

**Benchmark Definition**

The benchmark definition JSON provides information about the benchmark itself:
```json
{
  "Name": "startsWith vs indexOf vs endsWith",
  "Description": null,
  "Script Preparation Code": "var start = 'hello!';\r\nvar end = 'string!';\r\nvar string = start + ' im a ' + end; ",
  "Html Preparation Code": null
}
```
The script preparation code defines three variables: `start`, `end`, and `string`. The `string` variable is constructed by concatenating the `start` and `end` strings with an intermediate string.

**Test Cases**

The individual test cases are defined in a JSON array:
```json
[
  {
    "Benchmark Definition": "string.startsWith(start);",
    "Test Name": "startsWith"
  },
  {
    "Benchmark Definition": "string.indexOf(start) == 0;",
    "Test Name": "indexOf(start)"
  },
  {
    "Benchmark Definition": "string.endsWith(end);",
    "Test Name": "endsWith"
  },
  {
    "Benchmark Definition": "string.indexOf(end) == (string.length - end.length);",
    "Test Name": "indexOf(end)"
  }
]
```
Each test case defines a different benchmark definition, which is executed to measure its performance.

**Library and Syntax**

In the script preparation code, the `concat` method is used to concatenate strings:
```javascript
var string = start + ' im a ' + end;
```
The `concat` method returns a new string created by concatenating the individual arguments. This is not a native JavaScript function, but rather a part of the ECMAScript standard.

**Pros and Cons**

Here's a brief overview of each approach:

1. **startsWith**: This method checks if the string starts with the specified substring.
	* Pros: Simple and efficient, as it only needs to check the first few characters of the string.
	* Cons: May be slower for very long strings, as it has to iterate over the entire string.
2. **indexOf (with equality)**: This method checks if the index of the specified substring is equal to 0.
	* Pros: More efficient than `startsWith` for large strings, as it only needs to check a small portion of the string.
	* Cons: Requires an additional comparison with 0, which can be slower.
3. **endsWith**: This method checks if the string ends with the specified substring.
	* Pros: Similar to `startsWith`, but more efficient for very long strings, as it only needs to check the last few characters.
	* Cons: May be slower for short strings, as it has to iterate over the entire string.

**Alternatives**

Other alternatives could include:

1. **RegExp**: Using a regular expression with the `^` anchor can achieve similar results to `startsWith`. However, this approach may be slower and less efficient than the built-in methods.
2. **Substring extraction**: Extracting the substring using slicing or concatenation can also be used to implement these methods.

In summary, while each method has its pros and cons, `indexOf` (with equality) is generally the most efficient approach for checking if a string starts with or ends with a certain substring.

Related benchmarks:

startsWith vs indexOf vs endsWith (version: 0)

Comparing performance of: startsWith vs indexOf(start) vs endsWith vs indexOf(end)

Created: 4 years ago by: Registered User

Jump to the latest result

startsWith

indexOf(start)

endsWith

indexOf(end)

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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