下面的代码片段每次导入都会产生新的实例吗?
// 1st implementation
class ConnectionManager {
...
}
export default new ConnectionManager();
// 2nd implementation
class ConnectionManager {
...
}
const connectionManager = new ConnectionManager();
export default connectionManager;
如果是,如何在每次导入中获得相同的实例?
答案 0 :(得分:0)
在创建JavaScript模块以从模块中导出函数,对象或原始值时,将使用export语句,以便其他程序可以通过import语句使用它们。
有两种不同的导出类型,命名导出和默认导出。每个模块可以有多个命名导出,但是只有一个默认导出。
export default class ConnectionManager { .. }
或
class ConnectionManager {
...
}
export default connectionManager;
答案 1 :(得分:0)
ES6模块遵循单实例模式。也就是说,实例是在模块加载时创建的。
Here是关于它的文章。
// File: yolo.js class Yolo {} export let yolo = new Yolo(); // File: laser.js import { yolo } from "./yolo.js"; // yolo is a single instance of Yolo class // File: cat.js import { yolo } from "./yolo.js"; // same yolo as in laster.js
答案 2 :(得分:0)
应该相同。
以下示例使用这两种实现,将它们导入2个不同的文件,并将它们全部导入单个index
文件。每次创建实例时,我们都会为该类生成一个随机的value
,并记录其创建。
// ConnectionManagerImpl1.ts
class ConnectionManagerImpl1 {
public value;
constructor() {
this.value = Math.random().toString(36).substring(7);
console.log(`New ConnectionManagerImpl1 instance created: ${this.value}`)
}
}
export default new ConnectionManagerImpl1();
// ConnectionManagerImpl2.ts
class ConnectionManagerImpl2 {
public value;
constructor() {
this.value = Math.random().toString(36).substring(7);
console.log(`New ConnectionManagerImpl2 instance created: ${this.value}`)
}
}
const connectionManagerImpl2 = new ConnectionManagerImpl2();
export default connectionManagerImpl2;
// import1.ts
import connectionManagerImpl1 from './ConnectionManagerImpl1';
import connectionManagerImpl2 from './ConnectionManagerImpl2';
export { connectionManagerImpl1, connectionManagerImpl2 };
// import2.ts
import connectionManagerImpl1 from './ConnectionManagerImpl1';
import connectionManagerImpl2 from './ConnectionManagerImpl2';
export { connectionManagerImpl1, connectionManagerImpl2 };
// index.ts
import * as import1 from './import1';
import * as import2 from './import2';
console.log(import1)
console.log(import2)
console.log("Done")
使用tsc --module 'commonjs' * && node index.js
输出:
New ConnectionManagerImpl1 instance created: ddt3re
New ConnectionManagerImpl2 instance created: uv5z6
{ connectionManagerImpl1: ConnectionManagerImpl1 { value: 'ddt3re' },
connectionManagerImpl2: ConnectionManagerImpl2 { value: 'uv5z6' } }
{ connectionManagerImpl1: ConnectionManagerImpl1 { value: 'ddt3re' },
connectionManagerImpl2: ConnectionManagerImpl2 { value: 'uv5z6' } }
Done
如您所见,仅创建了ConnectionManagerImpl1
和ConnectionManagerImpl2
的1个实例。因此,两个实现都应该只创建一个实例。