iterWhileEach

Create an iterator which, while a test condition is true, invokes a function for each iterated value before returning the iterated value.

Usage

var iterWhileEach = require( '@stdlib/iter/while-each' );

iterWhileEach( iterator, predicate, fcn[, thisArg] )

Returns an iterator which invokes a function for each iterated value before returning the iterated value until either a predicate function returns false or the iterator has iterated over all values.

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

function predicate( v ) {
    return v < 3;
}

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

var it = iterWhileEach( array2iterator( [ 1, 2, 3, 4 ] ), predicate, assert );
// returns {}

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

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

r = it.next().value;
// undefined

// ...

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.

Both the predicate function and the function to invoke for each iterated value are provided two arguments:

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

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

function predicate( v ) {
    return v < 3;
}

function assert( v, i ) {
    if ( i > 1 ) {
        throw new Error( 'unexpected error' );
    }
}

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

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

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

r = it.next().value;
// undefined

// ...

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' );
    }
}

function predicate( v ) {
    return v < 3;
}

var ctx = {
    'count': 0
};

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

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

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

var count = ctx.count;
// returns 2

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 iterWhileEach = require( '@stdlib/iter/while-each' );

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

function predicate( v ) {
    return v <= 0.75;
}

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

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

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