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timeit

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]

Time a snippet.

## Installation

bash
npm install @stdlib/utils-timeit

Alternatively,

- To load the package in a website via a script tag without installation and bundlers, use the [ES Module][es-module] available on the [esm][esm-url] branch (see [README][esm-readme]).
- If you are using Deno, visit the [deno][deno-url] branch (see [README][deno-readme] for usage intructions).
- For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [umd][umd-url] branch (see [README][umd-readme]).
- To use as a general utility for the command line, install the corresponding [CLI package][cli-section] globally.

The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

## Usage

javascript
var timeit = require( '@stdlib/utils-timeit' );

#### timeit( code, [options,] clbk )

Times a snippet.

javascript
var code = 'var x = Math.pow( Math.random(), 3 );';
code += 'if ( x !== x ) {';
code += 'throw new Error( \'Something went wrong.\' );';
code += '}';

timeit( code, done );

function done( error, results ) {
    if ( error ) {
        throw error;
    }
    console.dir( results );
    /* e.g., =>
        {
            'iterations': 1000000,
            'repeats': 3,
            'min': [0,135734733],       // [seconds,nanoseconds]
            'elapsed': 0.135734733,     // seconds
            'rate': 7367311.062526641,  // iterations/second
            'times': [                  // raw timing results
                [0,145641393],
                [0,135734733],
                [0,140462721]
            ]
        }
    */
}

The function supports the following options:

- before: setup code. Default: "".
- after: cleanup code. Default: "".
- iterations: number of iterations. If null, the number of iterations is determined by trying successive powers of 10 until the total time is at least 0.1 seconds. Default: 1e6.
- repeats: number of repeats. Default: 3.
- asynchronous: boolean indicating whether a snippet is asynchronous. Default: false.

To perform any setup or initialization, provide setup code.

javascript
var setup = 'var randu = require( \'@stdlib/random-base-randu\' );';
setup += 'var pow = require( \'@stdlib/math-base-special-pow\' );';

var code = 'var x = pow( randu(), 3 );';
code += 'if ( x !== x ) {';
code += 'throw new Error( \'Something went wrong.\' );';
code += '}';

var opts = {
    'before': setup
};

timeit( code, opts, done );

function done( error, results ) {
    if ( error ) {
        throw error;
    }
    console.dir( results );
}

To perform any cleanup, provide cleanup code.

javascript
var setup = 'var randu = require( \'@stdlib/random-base-randu\' );';
setup += 'var hypot = require( \'@stdlib/math-base-special-hypot\' );';

var code = 'var h = hypot( randu()*10, randu()*10 );';
code += 'if ( h < 0 || h > 200 ) {';
code += 'throw new Error( \'Something went wrong.\' );';
code += '}';

var cleanup = 'if ( h !== h ) {';
cleanup += 'throw new Error( \'Something went wrong.\' );';
cleanup += '}';

var opts = {
    'before': setup,
    'after': cleanup
};

timeit( code, opts, done );

function done( error, results ) {
    if ( error ) {
        throw error;
    }
    console.dir( results );
}

To time an asynchronous snippet, set the asynchronous option to true.

javascript
var code = 'var x = Math.pow( Math.random(), 3 );';
code += 'if ( x !== x ) {';
code += 'var err = new Error( \'Something went wrong.\' );';
code += 'next( err );';
code += '}';
code += 'process.nextTick( next );';

var opts = {
    'iterations': 1e2,
    'asynchronous': true
};

timeit( code, opts, done );

function done( error, results ) {
    if ( error ) {
        throw error;
    }
    console.dir( results );
}

If asynchronous is true, the implementation assumes that before, after, and code snippets are all asynchronous. Accordingly, these snippets should invoke a next( [error] ) callback once complete. For example, given the following snippet,

javascript
setTimeout( done, 0 );

function done( error ) {
    if ( error ) {
        return next( error );
    }
    next();
}

the implementation wraps the snippet within a function having the following signature

javascript
function wrapped( state, next ) {
    setTimeout( done, 0 );

    function done( error ) {
        if ( error ) {
            return next( error );
        }
        next();
    }
}

The state parameter is simply an empty {} which allows the before, after, and code snippets to share state.

javascript
function before( state, next ) {
    state.counter = 0;
}

function code( state, next ) {
    setTimeout( done, 0 );

    function done( error ) {
        if ( error ) {
            return next( error );
        }
        state.counter += 1;
        next();
    }
}

function after( state, next ) {
    var err;
    if ( state.counter !== state.counter ) {
        err = new Error( 'Something went wrong!' );
        return next( err );
    }
    next();
}

## Notes

- Snippets always run in [strict mode][strict-mode].
- Always verify results. Doing so prevents the compiler from performing dead code elimination and other optimization techniques, which would render timing results meaningless.
- Executed code is not sandboxed and has access to the global state. You are strongly advised against timing untrusted code. To time untrusted code, do so in an isolated environment (e.g., a separate process with restricted access to both global state and the host environment).
- Wrapping asynchronous code does add overhead, but, in most cases, the overhead should be negligible compared to the execution cost of the timed snippet.
- Ensure that, when asynchronous is true, the main code snippet is actually asynchronous. If a snippet releases the [zalgo][zalgo], an error complaining about exceeding the maximum call stack size is highly likely.
- While many benchmark frameworks calculate various statistics over raw timing results (e.g., mean and standard deviation), do not do this. Instead, consider the fastest time an approximate lower bound for how fast an environment can execute a snippet. Slower times are more likely attributable to other processes interfering with timing accuracy rather than attributable to variability in JavaScript’s speed. In which case, the minimum time is most likely the only result of interest. When considering all raw timing results, apply common sense rather than statistics.

## Examples

javascript
var join = require( 'path' ).join;
var readFileSync = require( '@stdlib/fs-read-file' ).sync;
var timeit = require( '@stdlib/utils-timeit' );

var before = readFileSync( join( __dirname, 'examples', 'before.txt' ), 'utf8' );
var code = readFileSync( join( __dirname, 'examples', 'code.txt' ), 'utf8' );

var opts = {
    'iterations': 1e6,
    'repeats': 5,
    'before': before
};

timeit( code, opts, done );

function done( error, results ) {
    if ( error ) {
        throw error;
    }
    console.dir( results );
}

## CLI

## Installation

To use as a general utility, install the CLI package globally

bash
npm install -g @stdlib/utils-timeit-cli

### Usage

text
Usage: timeit [options] [<code>]

Options:

  -h,    --help                Print this message.
  -V,    --version             Print the package version.
         --iterations iter     Number of iterations.
         --repeats repeats     Number of repeats. Default: 3.
         --before setup        Setup code.
         --after cleanup       Cleanup code.
         --async               Time asynchronous code.
         --format fmt          Output format: pretty, csv, json. Default: pretty.

### Notes

- When the output format is csv, the output consists of only raw timing results.
- If not explicitly provided --iterations, the implementation tries successive powers of 10 until the total time is at least 0.1 seconds.

### Examples

bash
$ timeit "$(cat ./examples/code.txt)" --before "$(cat ./examples/before.txt)" --iterations 1000000

iterations: 1000000
repeats: 3
iterations/s: 7261975.851461222
elapsed time: 0.13770357 sec
lower bound: 0.13770357 usec/iteration

To output results as JSON,

bash
$ timeit "$(cat ./examples/code.txt)" --before "$(cat ./examples/before.txt)" --iterations 1000000 --format json
{"iterations":1000000,"repeats":3,"min":[0,132431806],"elapsed":0.132431806,"rate":7551056.1261997735,"times":[[0,142115140],[0,132431806],[0,134808376]]}

To output results as comma-separated values ([CSV][csv]),

bash
$ timeit "$(cat ./examples/code.txt)" --before "$(cat ./examples/before.txt)" --iterations 1000000 --format csv
seconds,nanoseconds
0,139365407
0,138033545
0,135175834

To use as part of a pipeline,

bash
$ cat ./examples/code.txt | timeit --before "$(cat ./examples/before.txt)" --iterations 1000000

iterations: 1000000
repeats: 3
iterations/s: 7433536.674260073
elapsed time: 0.134525468 sec
lower bound: 0.134525468 usec/iteration

## References

- Chen, Jiahao, and Jarrett Revels. 2016. “Robust benchmarking in noisy environments.” CoRR abs/1608.04295 (August). http://arxiv.org/abs/1608.04295.

*

## Notice

This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].

#### Community

[![Chat][chat-image]][chat-url]

—-

## License

See [LICENSE][stdlib-license].

## Copyright

Copyright © 2016-2024. The Stdlib [Authors][stdlib-authors].