Deno 程序的生命周期

Deno 支持浏览器兼容的生命周期事件 load 和 unload。可以使用这些事件在程序中提供用于安装(setup)和清理(cleanup)的代码

load事件的侦听器(listener)可以是异步(async)的，将被等待(await)。 ubload事件的监听器需要是同步的。这两项事件都不能被取消。

示例：

// main.ts
import "./imported.ts";

const handler = (e: Event): void => {
    console.log(`got ${e.type} event in event handler (main)` );
}

window.addEventListener("load", handler);

window.addEventListener("unload", handler);

window.onload = (e: Event): void => {
    console.log(`got ${e.type} event in onload function (main)`);
}

window.onunload = (e: Event): void => {
    console.log(`got ${e.type} event in onunload function (main)`);
}

console.log("log from main script")

// imported.ts
const handler = (e: Event): void => {
    console.log(`got ${e.type} event in event handler (imported)`);
}

window.addEventListener("load", handler);

window.addEventListener("unload", handler);

window.onload = (e: Event): void => {
    console.log(`got ${e.type} event in onload function (imported)`);
};

window.onunload = (e: Event): void => {
    console.log(`got ${e.type} event in onunload function (imported)`);
};

console.log("log from imported script");

运行结果：

$ deno run main.ts

log from imported script
log from main script
got load event in onload function (main)
got load event in event handler (imported)
got load event in event handler (main)
got unload event in onunload function (main)
got unload event in event handler (imported)
got unload event in event handler (main)

注意：你可以同时使用 window.addEventListener 和 window.onload / window.onunload 来定义事件的处理程序

但是它们之间有一个区别，如上面的运行结果，所有通过 window.addEventListener 添加的侦听器都被运行。 但是 main.ts中定义的 window.onload 和 window.onunload 覆盖了 imported.ts 中定义的处理程序