javascript - AngularJS - problems with $onChanges

I have an object defined in the parent ponent and passed in one-way binding to first-child and second-child ponents. First-child ponent make changes in the object. I cannot understand why in the second-child ponent $onChanges doesn't fire even if the object have changed something.

I have a project build as in this snippet (link to JSFiddle for pleteness)

angular.module('test', [])
ponent('parent', {
  template: "<first-child bind='vm.obj'></first-child>\
           <second-child bind='vm.obj'></second-child>\
    ",
  controller: function() {
    this.obj = {
      value: 0
    };
    this.$onInit = function() {}
  },
  controllerAs: 'vm',
  bindings: {}
})
ponent('firstChild', {
  template: "<button ng-click='vm.plus()'>+</button>\
           <button ng-click='vm.minus()'>-</button>\
          ",
  controller: function() {
    this.plus = function() {
      this.bind.value++;
    }

    this.minus = function() {
      this.bind.value--;
    }

    this.$onInit = function() {}

    this.$onChanges = function(obj) {
      console.log('first-child changed one-way bindings', obj)
    }
  },
  controllerAs: 'vm',
  bindings: {
    bind: '<'
  }
})
ponent('secondChild', {
  template: "<p>{{vm.bind.value}}</p>",
  controller: function() {
    this.$onInit = function() {}
    this.$onChanges = function(obj) {
      console.log('second-child changed one-way bindings', obj)
    }
  },
  controllerAs: 'vm',
  bindings: {
    bind: '<'
  }
})

<script src=".js/1.6.1/angular.min.js"></script>
<script src=".1.1/jquery.min.js"></script>

<body ng-app="test">
  <parent></parent>
</body>

I have a project build as in this snippet (link to JSFiddle for pleteness)

angular.module('test', [])
.ponent('parent', {
  template: "<first-child bind='vm.obj'></first-child>\
           <second-child bind='vm.obj'></second-child>\
    ",
  controller: function() {
    this.obj = {
      value: 0
    };
    this.$onInit = function() {}
  },
  controllerAs: 'vm',
  bindings: {}
})
.ponent('firstChild', {
  template: "<button ng-click='vm.plus()'>+</button>\
           <button ng-click='vm.minus()'>-</button>\
          ",
  controller: function() {
    this.plus = function() {
      this.bind.value++;
    }

    this.minus = function() {
      this.bind.value--;
    }

    this.$onInit = function() {}

    this.$onChanges = function(obj) {
      console.log('first-child changed one-way bindings', obj)
    }
  },
  controllerAs: 'vm',
  bindings: {
    bind: '<'
  }
})
.ponent('secondChild', {
  template: "<p>{{vm.bind.value}}</p>",
  controller: function() {
    this.$onInit = function() {}
    this.$onChanges = function(obj) {
      console.log('second-child changed one-way bindings', obj)
    }
  },
  controllerAs: 'vm',
  bindings: {
    bind: '<'
  }
})

<script src="https://cdnjs.cloudflare./ajax/libs/angular.js/1.6.1/angular.min.js"></script>
<script src="https://ajax.googleapis./ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<body ng-app="test">
  <parent></parent>
</body>

So my question is, is there a way to fire $onChanges in this situation?

$onChanges doesn't fire even if I define an array in parent, pass to first-child and second-child in one-way binding and in first-child I push something. But in that case the object has changed, so i still don't undertand why.

Share Improve this question edited Apr 29, 2023 at 20:05 ggorlen 57.4k8 gold badges111 silver badges154 bronze badges asked Apr 7, 2017 at 18:31 Matteo Meil 1,35311 silver badges22 bronze badges

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1 Answer 1

Sorted by: Reset to default 5

You are misunderstanding the usage of one-way binding a little.

One-way binding will trigger $onChanges if the object changes, but not if a property of the object changes.

You must bind directly to the value in secondChild, not the full object.

Here is a solution to your problem:

angular.module('test', [])
.ponent('parent', {
  template: "   <first-child bind='vm.obj'></first-child>\
                            <second-child value='vm.obj.value'></second-child>\
                        ",
  controller: function(){
    this.obj = {value: 0};
    this.$onInit = function(){}
    },
  controllerAs: 'vm',
  bindings: {}
})
.ponent('firstChild', {
    template: " <button ng-click='vm.plus()'>+</button>\
                            <button ng-click='vm.minus()'>-</button>\
                        ",
  controller: function(){
    
    this.plus = function(){
        this.bind.value++;
    }
    
    this.minus = function(){
        this.bind.value--;
    }
        
    this.$onInit = function(){}
        
    this.$onChanges = function(obj){
        console.log('first-child changed one-way bindings', obj)
        }
    },
  controllerAs: 'vm',
  bindings: {
    bind: '<'
  }
})
.ponent('secondChild', {
  template: "<p>{{vm.value}}</p>",
  controller: function(){
        this.$onInit = function(){}
        this.$onChanges = function(obj){
            console.log('second-child changed one-way bindings', obj)
        }
  },
  controllerAs: 'vm',
  bindings: {
    value: '<'
  }
})

Quick advice: I think you should work with two-way binding with firstChild, directly on the value, and then one-way in secondChild directly with value too.

Your fiddle with correction.

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javascript - AngularJS - problems with $onChanges - Stack Overflow

1 Answer 1

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