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doc: number documentation
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PR-URL: #356
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
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NickNaso authored and mhdawson committed Sep 28, 2018
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# Number

A Javascript number value.
`Napi::Number` class is a representation of the JavaScript `Number` object. The
`Napi::Number` class inherits its behavior from `Napi::Value` class
(for more info see [`Napi::Value`](value.md))

## Methods

### Constructor

Creates a new _empty_ instance of a `Napi::Number` object.

```cpp
Napi::Number();
```

Returns a new _empty_ `Napi::Number` object.

### Contructor

Creates a new instance of a `Napi::Number` object.

```cpp
Napi::Number(napi_env env, napi_value value);
```
- `[in] env`: The `napi_env` environment in which to construct the `Napi::Nuber` object.
- `[in] value`: The `napi_value` which is a handle for a JavaScript `Number`.
Returns a non-empty `Napi::Number` object.
### New
Creates a new instance of a `Napi::Number` object.
```cpp
Napi::Number Napi::Number::New(napi_env env, double value);
```
- `[in] env`: The `napi_env` environment in which to construct the `Napi::Nuber` object.
- `[in] value`: The `napi_value` which is a handle for a JavaScript `Number`.

Creates a new instance of a `Napi::Number` object.

### Int32Value

Converts a `Napi::Number` value to a `uint32_t` primitive type.

```cpp
Napi::Number::Int32Value() const;
```

Returns the `int32_t` primitive type of the corresponding `Napi::Number` object.

### Uint32Value

Converts a `Napi::Number` value to a `uint32_t` primitive type.

```cpp
Napi::Number::Uint32Value() const;
```

Returns the `uint32_t` primitive type of the corresponding `Napi::Number` object.

### Int64Value

Converts a `Napi::Number` value to a `int64_t` primitive type.

```cpp
Napi::Number::Int64Value() const;
```

Returns the `int64_t` primitive type of the corresponding `Napi::Number` object.

### FloatValue

Converts a `Napi::Number` value to a `float` primitive type.

```cpp
Napi::Number::New(Napi::Env env, double value);
Napi::Number::FloatValue() const;
```
- `[in] env`: The `napi_env` Environment
- `[in] value`: The value the Javascript Number will contain

Returns the `float` primitive type of the corresponding `Napi::Number` object.

### DoubleValue

Converts a `Napi::Number` value to a `double` primitive type.

```cpp
Napi::Number::Number();
Napi::Number::DoubleValue() const;
```
returns a new empty Javascript Number

You can easily cast a Javascript number to one of:
Returns the `double` primitive type of the corresponding `Napi::Number` object.

## Operators

The `Napi::Number` class contains a set of operators to easily cast JavaScript
`Number` object to one of the following primitive types:

- `int32_t`
- `uint32_t`
- `int64_t`
- `float`
- `double`

The following shows an example of casting a number to an uint32_t value.
### operator int32_t

Converts a `Napi::Number` value to a `int32_t` primitive.

```cpp
Napi::Number::operator int32_t() const;
```

Returns the `int32_t` primitive type of the corresponding `Napi::Number` object.

### operator uint32_t

Converts a `Napi::Number` value to a `uint32_t` primitive type.

```cpp
Napi::Number::operator uint32_t() const;
```

Returns the `uint32_t` primitive type of the corresponding `Napi::Number` object.

### operator int64_t

Converts a `Napi::Number` value to a `int64_t` primitive type.

```cpp
Napi::Number::operator int64_t() const;
```

Returns the `int64_t` primitive type of the corresponding `Napi::Number` object.

### operator float

Converts a `Napi::Number` value to a `float` primitive type.

```cpp
Napi::Number::operator float() const;
```

Returns the `float` primitive type of the corresponding `Napi::Number` object.

### operator double

Converts a `Napi::Number` value to a `double` primitive type.

```cpp
Napi::Number::operator double() const;
```

Returns the `double` primitive type of the corresponding `Napi::Number` object.

### Example

The following shows an example of casting a number to an `uint32_t` value.

```cpp
uint32_t operatorVal = Napi::Number::New(Env(), 10.0); // Number to unsigned 32 bit integer
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