*ngIf and *ngFor on same element causing error

How to Fix *ngIf and *ngFor on Same Element Error in Angular

If you've encountered an error when trying to use Angular's *ngIf and *ngFor directives on the same element, you're not alone! Many developers face this issue when attempting to loop through a collection using *ngFor, only to have the collection be seen as null when combined with an *ngIf condition.

The Problem

The error occurs because the *ngIf directive evaluates its condition before the *ngFor directive renders the elements. This means that when the *ngIf condition is false, the element that should be repeated by *ngFor is not present, causing Angular to see the collection as null.

In the provided example, the *ngFor loop is inside the *ngIf condition, making it susceptible to this error.

The Solution

Fortunately, there is an easy solution to resolve this issue. To avoid the error, you need to separate the *ngIf and *ngFor directives onto different elements.

Instead of having the *ngIf and *ngFor on the same <div> element, you can move the *ngIf to a higher-level element while keeping the *ngFor on the desired element:

<div *ngIf="show">
  <div *ngFor="let thing of stuff">
    {{ log(thing) }}
    <span>{{ thing.name }}</span>
  </div>
</div>

By doing this, the *ngIf condition will be evaluated first, and if it is true, the *ngFor directive will generate the intended elements without encountering the null issue.

The Plunker Example

To see the solution in action, you can check out the Plunker example provided in the question. By applying the changes mentioned above, the console error should no longer occur.

Conclusion

Encountering errors when trying to use *ngIf and *ngFor on the same element in Angular is a common issue. However, by separating these directives onto different elements, you can easily resolve the problem and ensure the smooth rendering of your templates.

Now that you know how to fix this error, go ahead and update your Angular code to prevent any future issues. Happy coding! 🚀

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