About stdlib...

We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.

The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.

When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.

To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!

iterForEach

Create an iterator which invokes a function for each iterated value before returning the iterated value.

Installation

npm install @stdlib/iter-for-each

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md 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

var iterForEach = require( '@stdlib/iter-for-each' );

iterForEach( iterator, fcn[, thisArg] )

Returns an iterator which invokes a function for each iterated value before returning the iterated value.

var array2iterator = require( '@stdlib/array-to-iterator' );

function assert( v ) {
    if ( v !== v ) {
        throw new Error( 'should not be NaN' );
    }
}

var it = iterForEach( array2iterator( [ 1, 2, 3, 4 ] ), assert );
// returns <Object>

var r = it.next().value;
// returns 1

r = it.next().value;
// returns 2

r = it.next().value;
// returns 3

// ...

The returned iterator protocol-compliant object has the following properties:

• next: function which returns an iterator protocol-compliant object containing the next iterated value (if one exists) assigned to a value property and a done property having a boolean value indicating whether the iterator is finished.
• return: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object.

The invoked function is provided two arguments:

• value: iterated value
• index: iteration index (zero-based)

var array2iterator = require( '@stdlib/array-to-iterator' );

function assert( v, i ) {
    if ( i < 0 ) {
        throw new Error( 'unexpected Error' );
    }
}

var it = iterForEach( array2iterator( [ 1, 2, 3, 4 ] ), assert );
// returns <Object>

var r = it.next().value;
// returns 1

r = it.next().value;
// returns 2

r = it.next().value;
// returns 3

// ...

To set the execution context for fcn, provide a thisArg.

var array2iterator = require( '@stdlib/array-to-iterator' );

function assert( v ) {
    this.count += 1;
    if ( v !== v ) {
        throw new Error( 'should not be NaN' );
    }
}

var ctx = {
    'count': 0
};

var it = iterForEach( array2iterator( [ 1, 2, 3, 4 ] ), assert, ctx );
// returns <Object>

var r = it.next().value;
// returns 1

r = it.next().value;
// returns 2

r = it.next().value;
// returns 3

var count = ctx.count;
// returns 3

Notes

• If an environment supports Symbol.iterator and a provided iterator is iterable, the returned iterator is iterable.

Examples

var randu = require( '@stdlib/random-iter-randu' );
var isnan = require( '@stdlib/math-base-assert-is-nan' );
var iterForEach = require( '@stdlib/iter-for-each' );

function assert( v ) {
    if ( isnan( v ) ) {
        throw new Error( 'should not be NaN' );
    }
}

// Create a seeded iterator for generating pseudorandom numbers:
var rand = randu({
    'seed': 1234,
    'iter': 10
});

// Create an iterator which validates generated numbers:
var it = iterForEach( rand, assert );

// Perform manual iteration...
var r;
while ( true ) {
    r = it.next();
    if ( r.done ) {
        break;
    }
    console.log( r.value );
}

---

See Also

• @stdlib/iter-map: create an iterator which invokes a function for each iterated value.

---

Notice

This package is part of 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, see the main project repository.

Community

---

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.