Mark Rajcok Mark Rajcok - 10 days ago 4
Javascript Question

Angular2 exception: Can't bind to 'ngForIn' since it isn't a known native property

What am I doing wrong?

import {bootstrap, Component} from 'angular2/angular2'

@Component({
selector: 'conf-talks',
template: `<div *ngFor="let talk in talks">
{{talk.title}} by {{talk.speaker}}
<p>{{talk.description}}
</div>`
})
class ConfTalks {
talks = [ {title: 't1', speaker: 'Brian', description: 'talk 1'},
{title: 't2', speaker: 'Julie', description: 'talk 2'}];
}
@Component({
selector: 'my-app',
directives: [ConfTalks],
template: '<conf-talks></conf-talks>'
})
class App {}
bootstrap(App, [])


The error is

EXCEPTION: Template parse errors:
Can't bind to 'ngForIn' since it isn't a known native property
("<div [ERROR ->]*ngFor="let talk in talks">

Answer

Since this is at least the third time I've wasted more than 5 min on this problem I figured I'd post the Q & A. I hope it helps someone else down the road... probably me!

I typed in instead of of in the ngFor expression. It should be:

<div *ngFor="#talk of talks">

Note that the ngFor syntax "desugars" into the following:

<template ngFor #talk [ngForOf]="talks">
  <div>...</div>
</template>

If we use in instead, it turns into

<template ngFor #talk [ngForIn]="talks">
  <div>...</div>
</template>

Since ngForIn isn't an attribute directive with an input property of the same name (like ngIf), Angular then tries to see if it is a (known native) property of the template element, and it isn't, hence the error.

UPDATE - as of beta.17, use the let syntax instead of #. This updates to the following:

<div *ngFor="let talk of talks">

Note that the ngFor syntax "desugars" into the following:

<template ngFor let-talk [ngForOf]="talks">
  <div>...</div>
</template>

If we use in instead, it turns into

<template ngFor let-talk [ngForIn]="talks">
  <div>...</div>
</template>
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