Angular 2: TypeError: l_thing0 is undefined in [{{thing.title}} in AppComponent@4:44]

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The issue is that the first time you load the page, thing is still undefined, it gets set to its real value later on asyncronously, so the first time it tries to access the property, it will throw an exception. The ? elvis operator is a shortcut to a nullcheck:

{{thing?.title}}

But its usually a best idea more performant not even try to render the component at all until you have the real object by adding something like:

<h1 *ngIf="thing">

to the container.

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