@stdlib/assert/is-duration-string/README.md

Standard assertion utilities.

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# isDurationString

> Test if a value is a duration string.

<section class="usage">

## Usage

```javascript
var isDurationString = require( '@stdlib/assert/is-duration-string' );
```

#### isDurationString( value )

Tests if a `value` is a duration `string`.

```javascript
var bool = isDurationString( '1d' );
// returns true

bool = isDurationString( '1d2h' );
// returns true
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   The function validates that a `value` is a `string`. For all other types, the function returns `false`.

-   A duration string is a string containing a sequence of time units. A time unit is a non-negative integer followed by a unit identifier. The following unit identifiers are supported:

    -   `d`: days
    -   `h`: hours
    -   `m`: minutes
    -   `s`: seconds
    -   `ms`: milliseconds

    For example, the string `1m3s10ms` is a duration string containing three time units: `1m` (1 minute), `3s` (3 seconds), and `10ms` (10 milliseconds). The string `60m` is a duration string containing a single time unit: `60m` (60 minutes). Time units must be supplied in descending order of magnitude (i.e., days, hours, minutes, seconds, milliseconds).

-   Duration strings are case insensitive. For example, the string `1M3S10MS` is equivalent to `1m3s10ms`.

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var isDurationString = require( '@stdlib/assert/is-duration-string' );

var bool = isDurationString( '1h' );
// returns true

bool = isDurationString( '1m20ms' );
// returns true

bool = isDurationString( '1d 2h 3m 4s' );
// returns false

bool = isDurationString( 'beep' );
// returns false

bool = isDurationString( null );
// returns false
```

</section>

<!-- /.examples -->

* * *

<section class="cli">

## CLI

<section class="usage">

### Usage

```text
Usage: is-duration-string [options] [<string>]

Options:

  -h,    --help                Print this message.
  -V,    --version             Print the package version.
         --split sep           Delimiter for stdin data. Default: '/\\r?\\n/'.
```

</section>

<!-- /.usage -->

<!-- CLI usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

### Notes

-   If the split separator is a [regular expression][mdn-regexp], ensure that the `split` option is either properly escaped or enclosed in quotes.

    ```bash
    # Not escaped...
    $ echo -n $'3m20s\n50ms' | is-duration-string --split /\r?\n/
    # Escaped...
    $ echo -n $'3m20s\n50ms' | is-duration-string --split /\\r?\\n/
    ```

-   The implementation ignores trailing delimiters.

</section>

<!-- /.notes -->

<section class="examples">

### Examples

```bash
$ is-duration-string '1h'
true
```

To use as a [standard stream][standard-streams],

```bash
$ echo -n '1x' | is-duration-string
false
```

By default, when used as a [standard stream][standard-streams], the implementation assumes newline-delimited data. To specify an alternative delimiter, set the `split` option.

```bash
$ echo -n '1h2m3s\tboop' | is-duration-string --split '\t'
true
false
```

</section>

<!-- /.examples -->

</section>

<!-- /.cli -->

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<section class="related">

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<section class="links">

[standard-streams]: https://en.wikipedia.org/wiki/Standard_streams

[mdn-regexp]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions

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</section>

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