单例模式

只允许实例化一次的对象类。

class Window {
    private static instance: Window;
    private constructor() { }
    static getInstance() {
        if (!Window.instance) {
            Window.instance = new Window();
        }
        return Window.instance;
    }
}
var w1 = Window.getInstance();
var w2 = Window.getInstance();
console.log(w1 === w2);

ES5单例模式

interface Window {
    hello: any
}
function Window() { }
Window.prototype.hello = function () {
    console.log('hello');
}
Window.getInstance = (function () {
    let window: Window;
    return function () {
        if (!window)
            window = new (Window as any)();
        return window;
    }
})();
let window = Window.getInstance();
window.hello();

透明单例

let Window = (function () {
    let window: Window;
    let Window = function (this: Window) {
        if (window) {
            return window;
        } else {
            return (window = this);
        }
    }
    Window.prototype.hello = function () {
        console.log('hello');
    }
    return Window;
})();
​
let window1 = new (Window as any)();
let window2 = new (Window as any)();
window1.hello();
console.log(window1 === window2)

封装变化

export { }
function Window() {
​
}
Window.prototype.hello = function () {
    console.log('hello');
}
​
let createInstance = function (Constructor: any) {
    let instance: any;
    return function (this: any) {
        if (!instance) {
            Constructor.apply(this, arguments);
            Object.setPrototypeOf(this, Constructor.prototype)
            instance = this;
        }
        return instance;
    }
};
let CreateWindow: any = createInstance(Window);
let window1 = new CreateWindow();
let window2 = new CreateWindow();
window1.hello();
console.log(window1 === window2

使用场景

redux store

• createStore.ts

function createStore(reducer: any) {
    let state: any;
    let listeners: any[] = [];
    function getState() {
        return state;
    }
    function dispatch(action: any) {
        state = reducer(state, action);
        listeners.forEach(l => l());
    }
    function subscribe(listener: any) {
        listeners.push(listener);
        return () => {
            listeners = listeners.filter(item => item != listener);
            console.log(listeners);
        }
    }
    dispatch({});
    return {
        getState,
        dispatch,
        subscribe
    }
}
let store = createStore((state: any, action: any) => state);

缓存

let express = require('express');
let fs = require('fs');
let cache: Record<any, any> = {};
let app = express();
app.get('/user/:id', function (req: any, res: any) {
    let id = req.params.id;
    let user = cache.get(id);
    if (user) {
        res.json(user);
    } else {
        fs.readFile(`./users/${id}.json`, 'utf8', function (err: any, data: any) {
            let user = JSON.parse(data);
            cache.put(id, user);
            res.json(user);
        });
    }
});
app.listen(3000);