我们平时阅读一些开源项目,可能会发现有些项目的package.json里的scripts区域定义的脚本很复杂,令人眼花缭乱。
其实这些脚本是有规律可循的。让我们从最简单的一个例子开始学习。
新建一个空文件夹,执行命令npm init,会自动在该文件夹下生成一个package.json。
![](https://img.laitimes.com/img/__Qf2AjLwojIjJCLyojI0JCLicmbw5iN2czM0cTZ3QTNxYjY5cjY1ATM0UGN3IDO4ITOxgTZh9CX5d2bs92Yl1iclB3bsVmdlR2LcNWaw9CXt92Yu4GZjlGbh5yYjV3Lc9CX6MHc0RHaiojIsJye.png)
{
"name": "nodejsexample",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"build": "node example.js",
"dev": "node example.js",
"start": "node example.js",
"prestart": "node example.js",
"poststart": "node example.js"
},
"author": "",
"license": "ISC"
}
然后我们再来编写example.js。为了简单起见,用example.js同时响应prestart, start和poststart三个事件,因此在example.js里需要判断当该文件执行时,到底所处哪个生命周期事件。这个可以用环境变量process.env.npm_lifecycle_event获得:
const ENVIRONMENT = process.env.npm_lifecycle_event;
if (ENVIRONMENT === "build") {
console.log("Running your build tasks!");
}
if ( ENVIRONMENT === "dev") {
console.log("Running the dev server!");同
}
if ( ENVIRONMENT === "prestart") {
console.log("Prestart event: Prepare for Start event!");
}
if ( ENVIRONMENT === "poststart") {
console.log("Poststart event: Do some cleanup task!");
}
if ( ENVIRONMENT === "start") {
console.log("Running App in production!");
}