此Javascript是否会导致内存泄漏？

Question

Notice in the following code, the child gets a reference to its parent. What happens when the original reference to parent is set to null? Does the parent stay around since there still is an active reference from the child?

Javascript

var parent = function() {
  var self = this;
  self.runme = function() {
    document.getElementById('output').innerText = 'run me';
  }

  self.child = new child(self);

  return self;
}
var child = function(parent) {
  var self = this;
  var parent = parent;
  self.event = function() {
    parent.runme();
  }
}
var p = new parent();
p.child.event();
p = null;

HTML

<div id="output">
  old value
</div>

FIDDLE https://jsfiddle.net/jeljeljel/8fvy5r4f/

Answer 1

var p = new parent();
p.child.event();
p = null;

Eventually both parent and child will be garbage collected because neither parent nor child will be "reachable" anymore. There's no memory leak here. That's assuming you are dealing with a modern JavaScript interpreter.

Answer 2

It shouldn't because most garbage collectors are based on the idea of reachability . Basically, if the object isn't reachable from the root(s) of the graph then it can be safely collected. After initialization you create a graph like this:

root -> parent <-> child

Then after p = null you get this:

root X parent <-> child

Since neither parent nor it's dependents are reachable, they can all be safely collected.