Angular 6.1 provides a new KeyValue pipe transforms Object or Map into an array of key value pairs. In the tutorial, we will show you how to iterate through Object, Map with KeyValue pipe.
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Contents
KeyValue Pipe
Transforms Object or Map into an array of key value pairs ->
{{ input_expression | keyvalue [ : compareFn ] }}
Input value
Input can be null, objects, or maps ->
null | { [key: string]: V; [key: number]: V; } | Map
Comparator Function
compareFn function is optional, used to sort the converted array based upon unicode point values of keys.
(a: KeyValue, b: KeyValue) => number
- keys are numbers -> sorted by ascending order.
- keys are strings -> sorted by alphabetical order.
- key is undefined or null -> displayed at last.
Angular KeyValue pipe has defaultComparator function to sort the key value array.
We can re-implement a new compareFn if our keys are complex types.
Practice
We create an Angular keyvalue-pipe component that uses KeyValue pipe to iterate through an Object and Map ->
KeyValuePipe Component class
keyvalue-pipe.component.ts ->
import { Component, OnInit } from '@angular/core'; @Component({ selector: 'app-keyvalue-pipe', templateUrl: './keyvalue-pipe.component.html' }) export class KeyvaluePipeComponent{ constructor() { } object: { [key: number]: string } = { 1: 'Property 1', 2: 'Property 2', 3: 'Property 3' }; map = new Map([ [4, 'Four'], [6, 'Six'], [5, 'Five'], ]); desc = (a, b) => { if(a.key < b.key) return b.key; } } |
KeyValuePipe style
keyvalue-pipe.component.html ->
<h3>Object with Keyvalue pipe</h3> <div *ngFor="let item of object | keyvalue"> key: {{item.key}} - value: {{item.value}} </div> <h3>Map with Keyvalue pipe - Desc Order</h3> <div *ngFor="let item of map | keyvalue:desc"> key: {{item.key}} - value: {{item.value}} </div> |
-> Results:
Sourcecode
Project structure ->
SourceCode:
Last updated on March 21, 2019.