I am a bit confused about how to get the key and value of an object in angular2 while using *ngFor for iterating over the object. I know in angular 1.x there is a syntax like
ng-repeat="(key, value) in demo"
but I don't know how to do the same in angular2. I have tried something similar, without success:
<ul>
<li *ngFor='#key of demo'>{{key}}</li>
</ul>
demo = {
'key1': [{'key11':'value11'}, {'key12':'value12'}],
'key2': [{'key21':'value21'}, {'key22':'value22'}],
}
Here is a plnkr with my attempt: http://plnkr.co/edit/mIj619FncOpfdwrR0KeG?p=preview
How can I get key1 and key2 dynamically using *ngFor? After searching extensively, I found the idea of using pipes but I don't know how to go about it.
Is there any inbuilt pipe for doing the same in angular2?
As in latest release of Angular (v6.1.0) , Angular Team has added new built in pipe for the same named as keyvalue pipe to help you iterate through objects, maps, and arrays, in the common module of angular package.
For example -
<div *ngFor="let item of testObject | keyvalue">
Key: <b>{{item.key}}</b> and Value: <b>{{item.value}}</b>
</div>
To keep original order, use keyvalue:onCompare,
and in component define callback:
// ...
import {KeyValue} from '@angular/common';
@Component(/* ... */)
export class MyComponent {
private onCompare(_left: KeyValue<any, any>, _right: KeyValue<any, any>): number {
return -1;
}
}
check it out here for more useful information -
If you are using Angular v5 or below or you want to achieve using pipe follow this answer
Have Object.keys accessible in the template and use it in *ngFor.
@Component({
selector: 'app-myview',
template: `<div *ngFor="let key of objectKeys(items)">{{key + ' : ' + items[key]}}</div>`
})
export class MyComponent {
objectKeys = Object.keys;
items = { keyOne: 'value 1', keyTwo: 'value 2', keyThree: 'value 3' };
constructor(){}
}
You could create a custom pipe to return the list of key for each element. Something like that:
import { PipeTransform, Pipe } from '@angular/core';
@Pipe({name: 'keys'})
export class KeysPipe implements PipeTransform {
transform(value, args:string[]) : any {
let keys = [];
for (let key in value) {
keys.push(key);
}
return keys;
}
}
and use it like that:
<tr *ngFor="let c of content">
<td *ngFor="let key of c | keys">{{key}}: {{c[key]}}</td>
</tr>
Edit
You could also return an entry containing both key and value:
@Pipe({name: 'keys'})
export class KeysPipe implements PipeTransform {
transform(value, args:string[]) : any {
let keys = [];
for (let key in value) {
keys.push({key: key, value: value[key]});
}
return keys;
}
}
and use it like that:
<span *ngFor="let entry of content | keys">
Key: {{entry.key}}, value: {{entry.value}}
</span>