JavaScript函数执行顺序

Question

Say you have the following three functions and variable

var someList = [];

makeObject() {

 // loops through someList here to create an object
 // then calls sendObject function

sendObject()

}

sendObject() {
 // sends object to database using HTTP call
}

resetList() {
 // resets the list to be empty
 // e.g. someList = []
}

Then you call them like so

makeObject()
resetList()

Is there any possiblity or any situation that the list will be reset before the makeObject function has a chance to loop through it?

Answer 1

There are plenty of things you can do in JavaScript which are asynchronous and non-blocking ( XMLHttpRequest and setTimeout are classic examples). If you use any of those inside makeObject then resetList will run before the asynchronous parts get called.

Answer 2

resetList() will be called directly after the HTTP call is made. Unless you do other async work before the HTTP call, the order will always be:

• makeObject()
• loop inside makeObject()
• sendObject() is called from inside makeObject()
• sendObject() does the HTTP call
• resetList() gets triggered right after the HTTP call since that HTTP call is async.
• The HTTP returns and any handlers attached to it are triggered.

But make sure that you don't do any other async work, else this will not apply.