什么是 newrelic？
newrelic 是一个性能管理工具，能够帮助开发者跟踪网站应用程序的性能。通过使用 newrelic，可以获取到应用程序的各种指标，例如响应时间、交易率、数据库请求等，并使用这些信息来优化应用程序，提高性能。
如何使用 newrelic？
下面将介绍如何使用 npm 包 newrelic 进行配置和使用。
步骤 1：安装 newrelic
在使用 newrelic 前，需要在项目中安装 newrelic 包。可通过以下命令在项目中安装它：
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步骤 2：配置 newrelic
在安装 newrelic 包后，需要对其进行配置，以便能够连接到 newrelic 服务器并跟踪应用程序的性能。
在项目的顶级目录中，新建一个名为 newrelic.js 的文件。该文件的基本结构如下：
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-其中，app_name 和 license_key 是使用 newrelic 服务所需要的名称和许可证密钥。newrelic 提供了两种设置方式：
- 环境变量：可以在项目中设置名为 NEW_RELIC_APP_NAME 和 NEW_RELIC_LICENSE_KEY 的环境变量。newrelic 可以自动检测到这些变量并将其用于配置。
- 配置文件：也可以使用 newrelic.js 文件中的值直接设置这些选项。在这种情况下，需要将环境变量设置为空。
这里提供一份配置文件的示例：
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-步骤 3：应用程序的代码
现在，需要将 newrelic 包添加到应用程序中，以便它可以跟踪应用程序的性能。
在 Chrome、Firefox 或 Safari 浏览器的窗口中打开应用程序，并通过插入以下代码将 newrelic 添加到应用程序中的头部：
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