CODEWITHSUNDEEP
javascript
mike
mike

Reputation: 859

Javascript Object watch

I use the next code for watch changes in javascript object: https://gist.github.com/eligrey/384583

I have a next code for check updates:

var Obj = {
    prop: 0,
    inc: function() {
      this.prop ++;
    }
};

Obj.watch('prop', function(prop, oldv, newv) {
    console.log(prop);
    console.log(oldv);
    console.log(newv);
  });

// on button click i increment prop:

$("#btn").on('click', function() {
    Obj.inc();
});

When i run this code, and click button i get in console:

prop
0 
1

It's correctly.

But, when i click the next time, i get:

z
undefined
NaN

Online demo: http://jsbin.com/jenarapufo/2/edit?html,js,console,output

Why?

Upvotes: 0

Views: 182

Answers (2)

James Hibbard
James Hibbard

Reputation: 17735

You'll need to return the new value from the callback:

Obj.watch('prop', function(prop, oldv, newv) {
  console.log(prop);
  console.log(oldv);
  console.log(newv);
  return newv;
});

Upvotes: 1

Evgeniy
Evgeniy

Reputation: 2921

You need to return new value from watch callback. Update Your handler:

Obj.watch('prop', function(prop, oldv, newv) {
    ...
    return newv;
})

Upvotes: 2

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