weakref service provider

weakref-service-provider.js

window.servicemap = new Map()

class A {
    constructor(){
        console.log("A created")
    }
}

function useService(A){
    let a = servicemap.get(A)
    if(!a){
        const newA = new A()
        servicemap.set(A, new WeakRef(newA))
        return newA
    }else{
        return a.deref()
    }
}

function wait(ms){
    return new Promise(resolve=>setTimeout(resolve, ms))
}

async function someView(){

    await wait(2000)
    const a = useService(A)

    await otherView()

    return a
}

async function otherView(){
    const a = useService(A)
    await wait(2000)
    return a
}

let time = 0
setInterval(()=>{
    console.log("at "+time+++" a is, ", servicemap.get(A)?.deref() ? "not null" : "null")
},1000)

someView().then(x=>{
    console.log('ended')
})