## 概述

`Number.POSITIVE_INFINITY` 属性表示正无穷大。

不必创建一个 `Number` 实例，可使用 `Number.POSITIVE_INFINITY` 来访问该静态属性。

`Number.POSITIVE_INFINITY` 属性的属性特性：
writable | false
enumerable | false
configurable | false

## 描述

`Number.POSITIVE_INFINITY` 的值同全局对象 `Infinity` 属性的值相同。

该值的表现同数学上的无穷大有点儿不同：

- 任何正值，包括 `POSITIVE_INFINITY`，乘以 `POSITIVE_INFINITY` 为 `POSITIVE_INFINITY`。
- 任何负值，包括 `NEGATIVE_INFINITY`，乘以 `POSITIVE_INFINITY` 为 `NEGATIVE_INFINITY`。
- 0 乘以 `POSITIVE_INFINITY` 为 NaN。
- NaN 乘以 `POSITIVE_INFINITY` 为 NaN。
- `POSITIVE_INFINITY` 除以 `NEGATIVE_INFINITY` 以外的任何负值为 `NEGATIVE_INFINITY`。
- `POSITIVE_INFINITY` 除以 `POSITIVE_INFINITY` 以外的任何正值为 `POSITIVE_INFINITY`。
- `POSITIVE_INFINITY` 除以 `NEGATIVE_INFINITY` 或 `POSITIVE_INFINITY` 为 NaN。
- 任何数除以 `POSITIVE_INFINITY` 为 0。

You might use the `Number.POSITIVE_INFINITY` property to indicate an error condition that returns a finite number in case of success. Note, however, that `isFinite` would be more appropriate in such a case.

## 示例

下例中，赋值给变量 `bigNumber` 一个大于 JavaScript 中最大值的值。当 `if` 语句执行时，变量 `bigNumber` 值为 "`Infinity`"， 因此在继续执行代码前，为变量 `bigNumber` 设置一个容易管理的值。

    var bigNumber = Number.MAX_VALUE * 2
    if (bigNumber == Number.POSITIVE_INFINITY) {
     bigNumber = returnFinite();
    }

## 规范

Specification | Status | Comment
--- | --- | ---
ECMAScript 1st Edition. Implemented in JavaScript 1.1 | Standard | Initial definition.
ECMAScript 5.1 (ECMA-262) Number.POSITIVE_INFINITY | Standard |
ECMAScript 2015 (6th Edition, ECMA-262) Number.POSITIVE_INFINITY | Standard |

## 浏览器兼容性

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Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari
--- | --- | --- | --- | --- | ---
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes)

Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile
--- | --- | --- | --- | --- | --- | ---
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes)

## 相关链接

- `Number.NEGATIVE_INFINITY`
- `Infinity`
- `isFinite`