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Dive into ngIf directive and ngShow directive with example


ngIf and ngShow directives are used very frequently in Angular apps. Here will the difference between these two through an example. Firstly, let's see the main difference between these two as in angular docs:
ngIf differs from ngShow and ngHide in that ngIf completely removes and recreates the element in the DOM rather then changing its visibility via display css property.
The main points are as follows:
  • ngShow directive uses css display property to show and hide the element in DOM. It does't remove the element from the DOM. It just set class="ng-hide" to hide the element and removes the ng-hide class to show the element.
  • ngIf directive remove and reinsert the element based on the expression provided in ng-if directive. The inserted element has the state which was initialized at the time of compilation.
  • If we change any css property of the element or set any class, that css property and class will be lost if the ng-if expression becomes false and the element is reinsert when the expression become true.
  • Similarly any event attached after the compilation will be lost when ng-if expression become false.
  • The css property, added class or any event attached will be there incase of ng-show or ng-hide directive.
  • When the element with ngIf directive is reinserted, it recreates a child scope which inherits from the parents scope. We should not redeclare primitive type within the ngIf element as it hide the parent primitive value. It cause two different values, one in parent and one in child scope. In such situation we should use object property within the element having ngIf directive. We can the object property without redeclaring it within the child scope as ng-model respond when the identity of the object changes, not when the property of object.
I have created and simple app to see how ng-if and ng-show directive responds:

 

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