@stdlib/iter/datespace/README.md

Standard iterator utilities.

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# iterDatespace

> Create an iterator which returns evenly spaced dates over a specified interval.

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## Usage

```javascript
var iterDatespace = require( '@stdlib/iter/datespace' );
```

#### iterDatespace( start, stop\[, N]\[, options] )

Returns an iterator which returns evenly spaced `Date` objects over a specified interval.

```javascript
var MILLISECONDS_IN_DAY = require( '@stdlib/constants/time/milliseconds-in-day' );

var start = ( new Date() ).getTime();
var it = iterDatespace( start, start+MILLISECONDS_IN_DAY );
// returns <Object>

var v = it.next().value;
// returns <Date>

v = it.next().value;
// returns <Date>

v = it.next().value;
// returns <Date>

// ...
```

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 function accepts the following `options`:

-   **round**: specifies how sub-millisecond times should be rounded: `'floor'`, `'ceil'`, or `'round'`. Default: `'floor'`.

By default, the iterator returns `100` values. To return an alternative number of values over the specified interval, provide an `N` argument.

```javascript
var MILLISECONDS_IN_DAY = require( '@stdlib/constants/time/milliseconds-in-day' );

var start = ( new Date() ).getTime();
var it = iterDatespace( start, start+MILLISECONDS_IN_DAY, 3 );
// returns <Object>

var v = it.next().value;
// returns <Date>

v = it.next().value;
// returns <Date>

v = it.next().value;
// returns <Date>

var bool = it.next().done;
// returns true
```

The returned iterator is guaranteed to return the `start` and `stop` values. Beware, however, that values between `start` and `stop` are subject to rounding errors. For example,

```javascript
var it = iterDatespace( 1417503655000, 1417503655001, 3 );
// returns <Object>

var v = it.next().value.getTime();
// returns 1417503655000

v = it.next().value.getTime();
// returns 1417503655000

v = it.next().value.getTime();
// returns 1417503655001
```

where sub-millisecond values are truncated by the `Date` constructor. Duplicate values should only be a problem when the interval separating consecutive times is less than a millisecond. As the interval separating consecutive dates goes to infinity, the quantization noise introduced by millisecond resolution is negligible.

By default, fractional timestamps are floored. To specify that timestamps always be rounded up or to the nearest millisecond when converted to `Date` objects, set the round option.

```javascript
var opts = {
    'round': 'ceil'
};
var it = iterDatespace( 1417503655000, 1417503655001, 3, opts );
// returns <Object>

var v = it.next().value.getTime();
// returns 1417503655000

v = it.next().value.getTime();
// returns 1417503655001

v = it.next().value.getTime();
// returns 1417503655001

opts = {
    'round': 'round'
};
it = iterDatespace( 1417503655000, 1417503655001, 3, opts );
// returns <Object>

v = it.next().value.getTime();
// returns 1417503655000

v = it.next().value.getTime();
// returns 1417503655001

v = it.next().value.getTime();
// returns 1417503655001
```

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<section class="notes">

## Notes

-   The `start` and `stop` arguments may be either `Date` objects, JavaScript timestamps (i.e., millisecond timestamps), or a valid date string.
-   If an environment supports `Symbol.iterator`, the returned iterator is iterable.

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## Examples

<!-- eslint no-undef: "error" -->

```javascript
var MILLISECONDS_IN_DAY = require( '@stdlib/constants/time/milliseconds-in-day' );
var HOURS_IN_DAY = require( '@stdlib/constants/time/hours-in-day' );
var iterDatespace = require( '@stdlib/iter/datespace' );

// Create an iterator which returns a Date object for each hour in the next 24 hours:
var start = new Date();
var end = new Date( start.getTime()+MILLISECONDS_IN_DAY );
var it = iterDatespace( start, end, HOURS_IN_DAY+1 );

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

</section>

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* * *

## See Also

-   <span class="package-name">[`@stdlib/array/from-iterator`][@stdlib/array/from-iterator]</span><span class="delimiter">: </span><span class="description">create (or fill) an array from an iterator.</span>
-   <span class="package-name">[`@stdlib/iter/incrspace`][@stdlib/iter/incrspace]</span><span class="delimiter">: </span><span class="description">create an iterator which returns evenly spaced numbers according to a specified increment.</span>
-   <span class="package-name">[`@stdlib/iter/linspace`][@stdlib/iter/linspace]</span><span class="delimiter">: </span><span class="description">create an iterator which returns evenly spaced numbers over a specified interval.</span>
-   <span class="package-name">[`@stdlib/iter/logspace`][@stdlib/iter/logspace]</span><span class="delimiter">: </span><span class="description">create an iterator which returns evenly spaced numbers on a log scale.</span>
-   <span class="package-name">[`@stdlib/iter/step`][@stdlib/iter/step]</span><span class="delimiter">: </span><span class="description">create an iterator which returns a sequence of numbers according to a specified increment.</span>

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[@stdlib/array/from-iterator]: https://www.npmjs.com/package/@stdlib/array-from-iterator

[@stdlib/iter/incrspace]: https://github.com/stdlib-js/iter/tree/main/incrspace

[@stdlib/iter/linspace]: https://github.com/stdlib-js/iter/tree/main/linspace

[@stdlib/iter/logspace]: https://github.com/stdlib-js/iter/tree/main/logspace

[@stdlib/iter/step]: https://github.com/stdlib-js/iter/tree/main/step

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</section>

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