npm package: @stdlib/napi-argv-double
Description: Convert a Node-API value to a double-precision floating-point number.
Author: The Stdlib Authors
Latest version: 0.2.2

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    About stdlib...
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# argv_double

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

> Convert a Node-API value to a double-precision floating-point number.

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/napi-argv-double
```

</section>

<section class="usage">

## Usage

```javascript
var headerDir = require( '@stdlib/napi-argv-double' );
```

#### headerDir

Absolute file path for the directory containing header files for C APIs.

```javascript
var dir = headerDir;
// returns <string>
```

</section>

<!-- /.usage -->

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<section class="notes">

</section>

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<!-- Package usage examples. -->

<section class="examples">

## Examples

```javascript
var headerDir = require( '@stdlib/napi-argv-double' );

console.log( headerDir );
// => <string>
```

</section>

<!-- /.examples -->

<!-- C interface documentation. -->

* * *

<section class="c">

## C APIs

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<section class="intro">

</section>

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<!-- C usage documentation. -->

<section class="usage">

### Usage

```c
#include "stdlib/napi/argv_double.h"
```

#### stdlib_napi_argv_double( env, value, \*out, \*message, \*err )

Converts a Node-API value to a double-precision floating-point number.

```c
#include "stdlib/napi/argv_double.h"
#include <node_api.h>

static napi_value addon( napi_env env, napi_callback_info info ) {
    napi_value value;

    // ...

    double out;
    napi_value err;
    napi_status status = stdlib_napi_argv_double( env, value, &out, "Must be a number.", &err );
    assert( status == napi_ok );
    if ( err != NULL ) {
        assert( napi_throw( env, err ) == napi_ok );
        return NULL;
    }

    // ...
}
```

The function accepts the following arguments:

-   **env**: `[in] napi_env` environment under which the function is invoked.
-   **value**: `[in] napi_value` Node-API value.
-   **out**: `[out] double*` destination for storing output value.
-   **message**: `[in] char*` error message.
-   **err**: `[out] napi_value*` pointer for storing a JavaScript error. If not provided a number, the function sets `err` with a JavaScript error; otherwise, `err` is set to `NULL`.

```c
napi_status stdlib_napi_argv_double( const napi_env env, const napi_value value, double *out, const char *message, napi_value *err );
```

The function returns a `napi_status` status code indicating success or failure (returns `napi_ok` if success).

#### STDLIB_NAPI_ARGV_DOUBLE( env, name, argv, index )

Macro for converting an add-on callback argument to a double-precision floating-point number.

```c
#include "stdlib/napi/argv_double.h"
#include "stdlib/napi/argv.h"
#include <node_api.h>

static double fcn( const double v ) {
    return v;
}

// ...

static napi_value addon( napi_env env, napi_callback_info info ) {
    // Retrieve add-on callback arguments:
    STDLIB_NAPI_ARGV( env, info, argv, argc, 1 );

    // Convert the first argument to a C type:
    STDLIB_NAPI_ARGV_DOUBLE( env, value, argv, 0 );

    // ...

    double out = fcn( value );
}
```

The macro expects the following arguments:

-   **env**: environment under which the callback is invoked.
-   **name**: output variable name.
-   **argv**: name of the variable containing add-on callback arguments.
-   **index**: argument index.

</section>

<!-- /.usage -->

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<section class="notes">

</section>

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<!-- C API usage examples. -->

<section class="examples">

</section>

<!-- /.examples -->

</section>

<!-- /.c -->

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</section>

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</section>

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<section class="main-repo" >

* * *

## Notice

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

#### Community

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---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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