Watch multiple scope attributes

Question

Is there a way to subscribe to events on multiple objects using  watch  E g    scope  watch  item1  item2   function

User · Answer

Why not simply wrap it in a forEach   angular forEach   a    b    c    function  key      scope  watch key  function  v        changed                It s about the same overhead as providing a function for the combined value  without actually having to worry about the value composition

User · Answer

A slightly safer solution to combine values might be to use the following as your  watch function   function     return angular toJson  item1  item2       or    scope  watch    function         return angular toJson  item1  item2           function            Stuff to do after either value changes

User · Answer

watch first parameter can also be a function    scope  watch function watchBothItems       return itemsCombinedValue       function whenItemsChange         stuff       If your two combined values are simple  the first parameter is just an angular expression normally   For example  firstName and lastName    scope  watch  firstName   lastName   function         stuff

User · Answer

watch first parameter can be angular expression or function  See documentation on  scope  watch  It contains a lot of useful info about how  watch method works  when watchExpression is called  how angular compares results  etc

User · Answer

Angular introduced  watchGroup in version 1 3 using which we can watch multiple variables  with a single  watchGroup block  watchGroup takes array as first parameter in which we can include all of our variables to watch    scope  watchGroup   var1   var2   function newVals oldVals      console log  new value of var1     newVals 0       console log  new value of var2     newVals 1       console log  old value of var1     oldVals 0       console log  old value of var2     oldVals 1

User · Answer

Beginning with AngularJS 1 1 4 you can use  watchCollection    scope  watchCollection   item1  item2    function newValues  oldValues          do stuff here        newValues and oldValues contain the new and respectively old value        of the observed collection array       Plunker example here  Documentation here

User · Answer

how about   scope  watch function         return          a  thing-one         b  thing-two         c  red-fish         d  blue-fish            listener

User · Answer

Here s a solution very similar to your original pseudo-code that actually works    scope  watch   item1  item2    json   function            EDIT  Okay  I think this is even better    scope  watch   item1  item2    function         true     Basically we re skipping the json step  which seemed dumb to begin with  but it wasn t working without it   They key is the often omitted 3rd parameter which turns on object equality as opposed to reference equality    Then the comparisons between our created array objects actually work right

User · Answer

scope  watch  age   name   function          called when name or age changed       Here function will get called when both age and name value get changed

User · Answer

Starting from AngularJS 1 3 there s a new method called  watchGroup for observing a set of expressions    scope foo    foo    scope bar    bar     scope  watchGroup   foo    bar    function newValues  oldValues  scope         newValues array contains the current values of the watch expressions      with the indexes matching those of the watchExpression array      i e       newValues 0  - gt   scope foo       and       newValues 1  - gt   scope bar

User · Answer

You can use functions in  watchGroup to select fields of an object in scope            scope  watchGroup           function      return  this  scope ViewModel Monitor1Scale                 function      return  this  scope ViewModel Monitor2Scale                 function  newVal  oldVal  scope                           if  newVal    oldVal                      this updateMonitorScales

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