JS中实现析构函数的最佳方法

Question

Consider the code below

class Hello {
    constructor(name) {
        this.interval = setInterval(() => {
            console.log('===', name)
        }, 1000)
    }
    destroy() {
        clearInterval(this.interval)
    }
}
let h = new Hello('aaa')
// h.destory()
h = new Hello('bbb')

If the constructor allocate some resource, where to release the resource? As far as I current understanding, when h is re-assigned to new Hello('bbb') to memory holding new Hello('aaa') should be released by GC .

Is this a good convention that new and destroy should come in pair?

Answer 1

Unfortunately there is no way (i believe) to catch the garbage collection of an object to perform some action. Instead you need to build your own management for cleaning up resources like timers, etc. by making your creations/removals explicit. I know your example is a toy, but you can't simply reallocate in the way you have shown. You need to do something like:

const objects = {}

const createObject = name => {
  const obj = new Hello(name)
  objects[name] = obj
  return obj
}

const deleteObject = name => {
  objects[name].destroy()
  delete objects[name]
}

let h = createObject('aaa')
deleteObject('aaa') // interval cleared but not gc'd because of h
h = createObject('bbb') // all references to aaa now gone

Obviously this is a simple example, and there will be more elegant ways to do it depending on your needs, but hopefully you get the idea.