HTML check variable undefined with ngIf excluding case when value is 0

Question

I am using Angular 2 and would like to check if a variable value is undefined using the htm *ngIf condition.

If I use <span *ngIf="!testvar">, it also covers the case when variable testvar = 0, but I would like to exclude the case when it is 0.

The following works, but those are 2 checks:

<span *ngIf="!testvar && testvarl != 0"></span>

I would like to check this case with only condition to shorten it and make it cleaner.

Is there a simple way to do this?

score 53 · Answer 1 · edited Mar 04 '19 at 22:37

53

You can just write:

*ngIf="testvar !== undefined"

edited Mar 04 '19 at 22:37

Alexander Abakumov

13,617
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answered Aug 22 '17 at 22:06

diopside

2,981
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daxtersky · Answer 2 · 2020-04-09T13:56:15.930

4

And if you might be worried about null too:

*ngIf="testvar !== undefined && testvar !== null"

edited Apr 09 '20 at 13:56

answered Apr 09 '20 at 13:48

daxtersky

410
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1

This can be shortened to `*ngIf="testvar != undefined"` – Marty Jun 10 '20 at 04:56
3

I believe this could also be `*ngIf="!!testvar"` – M Akin Oct 30 '20 at 18:49
1

no because that will also kill the 0, because 0 is falsy and that is the whole point of the question. – Woozar Sep 05 '22 at 11:38

score 2 · Answer 3 · answered Jan 12 '21 at 09:33

2

<ng-template [ngIf]="!!foo">
  <p>Hello World</p>
</ng-template>

"Hello World" will be hidden if foo is the undefined or null or empty string and it will show Hello World if the foo is a number or boolean is true or string or array or object.

answered Jan 12 '21 at 09:33

Vinod M

29
2

This will also be false if "foo" is number 0. And [ngIf] should be *ngIf – Lord Midi Mar 09 '21 at 10:42

score 0 · Answer 4 · answered Jun 11 '21 at 00:39

0

Despite, this is an old topic, this is a possible solution that can help others:

<span *ngIf="isValid(testvar)"></span>

isValid(str: String) {
    return typeof str !== 'undefined' && str != 0;
}

answered Jun 11 '21 at 00:39

gilbriatore

658
7
12

You don't want to use functions in your template like that, for performance – Rafael Oliveira Jun 22 '23 at 00:57

HTML check variable undefined with ngIf excluding case when value is 0

4 Answers4