我們平時閱讀一些開源項目,可能會發現有些項目的package.json裡的scripts區域定義的腳本很複雜,令人眼花缭亂。
其實這些腳本是有規律可循的。讓我們從最簡單的一個例子開始學習。
建立一個空檔案夾,執行指令npm init,會自動在該檔案夾下生成一個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"
}
然後我們再來編寫example.js。為了簡單起見,用example.js同時響應prestart, start和poststart三個事件,是以在example.js裡需要判斷當該檔案執行時,到底所處哪個生命周期事件。這個可以用環境變量process.env.npm_lifecycle_event獲得:
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!");
}