How to create a copy of the initial state of an array?

Question

I have ratings, that get fetched from a postgres database and displayed in a table. When I edit a rating, I can only add or remove tags to it through a input like element which comes from my "TagInputComponent".

The TagInputComponent looks like this:

import { Component, DoCheck, IterableDiffers, OnInit, Input, Output } from 'angular2/core';
import * as _ from 'underscore';

@Component({
    selector: 'taginput',
    templateUrl: 'app/shared/taginput.component.html',
    styleUrls: ['assets/stylesheets/taginput.css']
})
export class TagInputComponent implements OnInit, DoCheck {
@Input() tags: string[];
newTag = '';
oldTags: string[];
differ: any;

constructor(differs: IterableDiffers) { 
    this.differ = differs.find([]).create(null);
}

ngOnInit() { }

ngDoCheck() {
    var changes = this.differ.diff(this.tags);

    if (changes) {
        changes.forEachAddedItem(r => console.log('added ' + r.item));
        changes.forEachRemovedItem(r => console.log('removed ' + r.item));
    }
}

It gets used in the DataFormComponenet like this:

<taginput [tags]="datapoint.tags"></taginput>

How do I create a copy of tags to oldTags once it is filled with data?

It noticed that ngOnInit() is too early as the data is not yet there from the service. With ngDoCheck() it always updates to the currentState.

It seems like a simple task, but I just can't find out how to do it.

igorzg answer worked for me, although I changed it to my needs. This is what I did:

ngDoCheck() {
    var changes = this.differ.diff(this.tags);

    if (changes) {
        if (Array.isArray(changes.collection) && !this.oldTags) {
            this.oldTags = changes.collection.slice();
        }

        changes.forEachAddedItem(r => console.log('added ' + r.item));
        changes.forEachRemovedItem(r => console.log('removed ' + r.item));
    }
}

igorzg · Accepted Answer · 2016-05-12 11:09:27Z

3

ngOnChanges(changes) {
   if (Array.isArray(changes.tags) && !this.oldTags) {
     this.oldTags = changes.tags.slice();
   }
}

answered May 12, 2016 at 11:09

igorzg

1,50614 silver badges17 bronze badges

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Comments

Artur Górski · Accepted Answer · 2016-05-12 11:50:47Z

1

How about setter?

@Input()
set tags(tags: string[]) {
  this.oldTags = tags.slice();
  _tags = tags;
}

edited May 12, 2016 at 11:50

answered May 12, 2016 at 11:08

Artur Górski

2,4532 gold badges17 silver badges14 bronze badges

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