Javascript-在检查对象属性存在时避免异步竞争条件

Question

Whilst JavaScript might not be multi-threaded, it does support asynchronous execution and whilst executions for 2 or more asynchronous bits of code might be on the same thread, the fact that an asynchronous order of events cannot be predicted, makes it possible for a race condition between asynchronous executions to occur.

I am doing an asynchronous check for the existence of an object property. Said property will be assigned a large multi-dimensional child object - including child objects arrays, own properties etc.

In the example below, I already know the parent object exists, ie I know that myObject exists. I want my check to return true as soon as all the content of myObject['myObjectChildren'] is in place.

To check for the existence of the object property, I do the following:

if(myObject.hasOwnProperty('myObjectChildren'))
    return true;

The only way that myObject['myObjectChildren'] gets assigned is in the format, but this assignment is done asynchronously:

myObject['myObjectChildren'] = {
          largeChildObject:{
              grandchildren:[
                   {grandchild1:{
                       grandchild1GreatGrandChildren:[
                              grandchild1GreatGrandChild1:{},
                              grandchild1GreatGrandChild2:{}....
                       ]
                   },
                   {grandchild2:{},
                   {grandchild3:{}....
              ]
           }
 };

MY QUESTION:

My question is, can I safely assume that as soon as myObject.hasOwnProperty('myObjectChildren') === true , myObject['myObjectChildren'] has all the content assigned to it, bearing in mind it is assigned in one go. Is there any circumstance where the check might fail? eg on assignment, does the property get instantiated to 'undefined' first?

Currently, my code is only returning true when all content for it is in place. However, my concern is that I've inadvertently entered into a race condition.

Answer 1

由于javascript执行具有单线程性质，因此在所有值均分配到一个同步块中的情况下，在所有情况下您的检查都是正确的，因为执行分配时控制流无法“跳转”到您的检查逻辑。