Backbone.js trigger event blocks the subsequent statement

Question

 obj1.listen(obj2, 'save', function(t) {
   t.preventDefault()
 })
 obj2 = {
   save: function save(a) {

     var saveOrNot = !1;
     this.trigger("save", {
       preventDefault: function() {
         saveOrNot = !0
       }
     });

     console.log("prevent default after")
     if (!saveOrNot) {
       console.log("got excuted")
     }

   }
 }

In my opinion, the line after the trigger line always gets executed because the preventDefault() doesn't get executed immediately. But the "got executed" message does not print. Does the code hang when triggering an event?

You say this gets printed, that doesn't etc. The code you shared has syntax errors and isn't runnable. What is `listen`..? What type of backbone objects are these..? Please read [ask] and [mcve] — T J, Jan 26 '16 at 18:04

score 0 · Accepted Answer · answered Jan 25 '16 at 13:49

It's not executed because each time when you run the preventDefault function you set the saveOrNot value to true, but when you check for this value condition it's always false, hence the console log is never executed.

if (!saveOrNot) { // this is the line in scope => this is always false
    console.log("got excuted")
}

If you want to change the value condition to it's opposite state it's better to use negation:

saveOrNot = !saveOrNot;

I would rewrite your code in the below manner:

obj1.listen(obj2, 'save', function(t) {
   t.preventDefault()
 })
 obj2 = {
   save: function save(a) {

     var saveOrNot = 0;
     this.trigger("save", {
       preventDefault: function() {
         saveOrNot = !saveOrNot;
       }
     });

     console.log("prevent default after")
     if (!saveOrNot) {
       console.log("got excuted")
     }

   }
 }

Honestly, you may not got what i am confused. The trigger and listen mechanism is asynchronous ？ — Chales Tuang, Jan 26 '16 at 12:11
You trigger an event and listen for an event. Why should be asynchronous? — Endre Simo, Jan 26 '16 at 13:53

Backbone.js trigger event blocks the subsequent statement

1 Answers1