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?

Universalize

Answer 1

You can just write:

*ngIf="testvar !== undefined"

Collaborative

Answer 2

And if you might be worried about null too:

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

Gris

This can be shortened to *ngIf="testvar != undefined" – Pulmonary

I believe this could also be *ngIf="!!testvar" – Hullo

no because that will also kill the 0, because 0 is falsy and that is the whole point of the question. – Fireboard

Answer 3

<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.

Defalcate

This will also be false if "foo" is number 0. And [ngIf] should be *ngIf – Esta

Answer 4

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;
}

Defilade

You don't want to use functions in your template like that, for performance – Cuss