README

forEach Iterator

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

Installation

npm install @stdlib/iter-for-each

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 ) {
    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

// ...

To set the function execution context, 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' );

var rand;
var it;
var r;

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

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

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

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

@stdlib/iter-for-each

Usage no npm install needed!