'Angular 2 - NgFor using numbers instead collections
...for example...
<div class="month" *ngFor="#item of myCollection; #i = index">
...
</div>
Is possible to do something like...
<div class="month" *ngFor="#item of 10; #i = index">
...
</div>
...without appeal to a non elegant solution like:
<div class="month" *ngFor="#item of ['dummy','dummy','dummy','dummy','dummy',
'dummy','dummy','dummy']; #i = index">
...
</div>
?
Solution 1:[1]
Within your component, you can define an array of number (ES6) as described below:
export class SampleComponent {
constructor() {
this.numbers = Array(5).fill().map((x,i)=>i); // [0,1,2,3,4]
this.numbers = Array(5).fill(4); // [4,4,4,4,4]
}
}
See this link for the array creation: Tersest way to create an array of integers from 1..20 in JavaScript.
You can then iterate over this array with ngFor:
@Component({
template: `
<ul>
<li *ngFor="let number of numbers">{{number}}</li>
</ul>
`
})
export class SampleComponent {
(...)
}
Or shortly:
@Component({
template: `
<ul>
<li *ngFor="let number of [0,1,2,3,4]">{{number}}</li>
</ul>
`
})
export class SampleComponent {
(...)
}
Solution 2:[2]
@OP, you were awfully close with your "non-elegant" solution.
How about:
<div class="month" *ngFor="let item of [].constructor(10); let i = index">
...
</div>
Here I'm getting the Array constructor from an empty array: [].constructor, because Array isn't a recognized symbol in the template syntax, and I'm too lazy to do Array=Array or counter = Array in the component typescript like @pardeep-jain did in his 4th example. And I'm calling it without new because new isn't necessary for getting an array out the Array constructor.
Array(30) and new Array(30) are equivalent.
The array will be empty, but that doesn't matter because you really just want to use i from ;let i = index in your loop.
Edit to respond to comments:
Q. How can I use a variable to set the length of the NgFor loop?
Here is an example on how to render a table with variable columns/rows
<table class="symbolTable">
<tr *ngFor="let f of [].constructor(numRows); let r = index">
<td class="gridCell" *ngFor="let col of [].constructor(numCols); let c = index">
{{gridCards[r][c].name}}
</td>
</tr>
</table>
export class AppComponent implements OnInit {
title = 'simbologia';
numSymbols = 4;
numCols = 5;
numRows = 5;
guessCards: SymbolCard[] = [];
gridCards: SymbolCard[][] = [];
ngOnInit(): void {
for (let c = 0; c < this.numCols; c++) {
this.guessCards.push(new SymbolCard());
}
for (let r = 0; r < this.numRows; r++) {
let row: SymbolCard[] = [];
for (let c = 0; c < this.numCols; c++) {
row.push(
new SymbolCard({
name: '' + r + '_' + c
}))
}
this.gridCards.push(row);
}
}
}
Solution 3:[3]
No there is no method yet for NgFor using numbers instead collections, At the moment, *ngFor only accepts a collection as a parameter, but you could do this by following methods:
Using pipe
demo-number.pipe.ts:
import {Pipe, PipeTransform} from 'angular2/core';
@Pipe({name: 'demoNumber'})
export class DemoNumber implements PipeTransform {
transform(value, args:string[]) : any {
let res = [];
for (let i = 0; i < value; i++) {
res.push(i);
}
return res;
}
}
For newer versions you'll have to change your imports and remove args[] parameter:
import { Pipe, PipeTransform } from '@angular/core';
@Pipe({name: 'demoNumber'})
export class DemoNumber implements PipeTransform {
transform(value) : any {
let res = [];
for (let i = 0; i < value; i++) {
res.push(i);
}
return res;
}
}
html:
<ul>
<li>Method First Using PIPE</li>
<li *ngFor='let key of 5 | demoNumber'>
{{key}}
</li>
</ul>
Using number array directly in HTML(View)
<ul>
<li>Method Second</li>
<li *ngFor='let key of [1,2]'>
{{key}}
</li>
</ul>
Using Split method
<ul>
<li>Method Third</li>
<li *ngFor='let loop2 of "0123".split("")'>{{loop2}}</li>
</ul>
Using creating New array in component
<ul>
<li>Method Fourth</li>
<li *ngFor='let loop3 of counter(5) ;let i= index'>{{i}}</li>
</ul>
export class AppComponent {
demoNumber = 5 ;
counter = Array;
numberReturn(length){
return new Array(length);
}
}
Solution 4:[4]
I couldn't bear the idea of allocating an array for plain repeat of components, so I've written a structural directive. In simplest form, that doesn't make the index available to the template, it looks like this:
import { Directive, Input, TemplateRef, ViewContainerRef } from '@angular/core';
@Directive({ selector: '[biRepeat]' })
export class RepeatDirective {
constructor( private templateRef: TemplateRef<any>,
private viewContainer: ViewContainerRef) { }
@Input('biRepeat') set count(c:number) {
this.viewContainer.clear();
for(var i=0;i<c;i++) {
this.viewContainer.createEmbeddedView(this.templateRef);
}
}
}
Solution 5:[5]
This can also be achieved like this:
HTML:
<div *ngFor="let item of fakeArray(10)">
...
</div>
Typescript:
fakeArray(length: number): Array<any> {
if (length >= 0) {
return new Array(length);
}
}
Solution 6:[6]
you can also use like that
export class SampleComponent {
numbers:Array<any> = [];
constructor() {
this.numbers = Array.from({length:10},(v,k)=>k+1);
}
}
HTML
<p *ngFor="let i of numbers">
{{i}}
</p>
Solution 7:[7]
Use a pipe to transform the number to an array.
@Pipe({
name: 'enumerate',
})
export class EnumeratePipe implements PipeTransform {
transform(n: number): number[] {
return [...Array(n)].map((_,i) => i);
}
}
Then use the pipe in your template.
<p *ngFor="let i of 5 | enumerate">
Index: {{ i }}
</p>
https://stackblitz.com/edit/angular-ivy-pkwvyw?file=src/app/app.component.html
Solution 8:[8]
I solved it like this using Angular 5.2.6 and TypeScript 2.6.2:
class Range implements Iterable<number> {
constructor(
public readonly low: number,
public readonly high: number,
public readonly step: number = 1
) {
}
*[Symbol.iterator]() {
for (let x = this.low; x <= this.high; x += this.step) {
yield x;
}
}
}
function range(low: number, high: number) {
return new Range(low, high);
}
It can be used in a Component like this:
@Component({
template: `<div *ngFor="let i of r">{{ i }}</div>`
})
class RangeTestComponent {
public r = range(10, 20);
}
Error checking and assertions omitted on purpose for brevity (e.g. what happens if step is negative).
Solution 9:[9]
You can use lodash:
@Component({
selector: 'board',
template: `
<div *ngFor="let i of range">
{{i}}
</div>
`,
styleUrls: ['./board.component.css']
})
export class AppComponent implements OnInit {
range = _.range(8);
}
I didn't test code but it should work.
Solution 10:[10]
<div *ngFor="let number of [].constructor(myCollection)">
<div>
Hello World
</div>
</div>
This is a nice and quick way to repeat for the amount of times in myCollection.
So if myCollection was 5, Hello World would be repeated 5 times.
Solution 11:[11]
Since the fill() method (mentioned in the accepted answer) without arguments throw an error, I would suggest something like this (works for me, Angular 7.0.4, Typescript 3.1.6)
<div class="month" *ngFor="let item of items">
...
</div>
In component code:
this.items = Array.from({length: 10}, (v, k) => k + 1);
Solution 12:[12]
My-component.ts
numbers: number[] = [];
constructor() {
this.numbers = new Array<number>(10)
}
My-component.html
<div *ngFor="let num of numbers; let i = index">{{ i }}</div>
Solution 13:[13]
Using custom Structural Directive with index:
According Angular documentation:
createEmbeddedViewInstantiates an embedded view and inserts it into this container.
abstract createEmbeddedView(templateRef: TemplateRef, context?: C, index?: number): EmbeddedViewRef.Param Type Description templateRef TemplateRef the HTML template that defines the view. context C optional. Default is undefined. index number the 0-based index at which to insert the new view into this container. If not specified, appends the new view as the last entry.
When angular creates template by calling createEmbeddedView it can also pass context that will be used inside ng-template.
Using context optional parameter, you may use it in the component, extracting it within the template just as you would with the *ngFor.
app.component.html:
<p *for="number; let i=index; let c=length; let f=first; let l=last; let e=even; let o=odd">
item : {{i}} / {{c}}
<b>
{{f ? "First,": ""}}
{{l? "Last,": ""}}
{{e? "Even." : ""}}
{{o? "Odd." : ""}}
</b>
</p>
for.directive.ts:
import { Directive, Input, TemplateRef, ViewContainerRef } from '@angular/core';
class Context {
constructor(public index: number, public length: number) { }
get even(): boolean { return this.index % 2 === 0; }
get odd(): boolean { return this.index % 2 === 1; }
get first(): boolean { return this.index === 0; }
get last(): boolean { return this.index === this.length - 1; }
}
@Directive({
selector: '[for]'
})
export class ForDirective {
constructor(private templateRef: TemplateRef<any>, private viewContainer: ViewContainerRef) { }
@Input('for') set loop(num: number) {
for (var i = 0; i < num; i++)
this.viewContainer.createEmbeddedView(this.templateRef, new Context(i, num));
}
}
Solution 14:[14]
Please find attached my dynamic solution if you want to increase the size of an array dynamically after clicking on a button (This is how I got to this question).
Allocation of necessary variables:
array = [1];
arraySize: number;
Declare the function that adds an element to the array:
increaseArrayElement() {
this.arraySize = this.array[this.array.length - 1 ];
this.arraySize += 1;
this.array.push(this.arraySize);
console.log(this.arraySize);
}
Invoke the function in html
<button md-button (click)="increaseArrayElement()" >
Add element to array
</button>
Iterate through array with ngFor:
<div *ngFor="let i of array" >
iterateThroughArray: {{ i }}
</div>
Solution 15:[15]
A simplest way that i have tried
You can also create an array in your component file and you can call it with *ngFor directive by returning as an array .
Something like this ....
import { Component, OnInit } from '@angular/core';
@Component({
selector: 'app-morning',
templateUrl: './morning.component.html',
styleUrls: ['./morning.component.css']
})
export class MorningComponent implements OnInit {
arr = [];
i: number = 0;
arra() {
for (this.i = 0; this.i < 20; this.i++) {
this.arr[this.i]=this.i;
}
return this.arr;
}
constructor() { }
ngOnInit() {
}
}
And this function can be used in your html template file
<p *ngFor="let a of arra(); let i= index">
value:{{a}} position:{{i}}
</p>
Solution 16:[16]
My solution:
export class DashboardManagementComponent implements OnInit {
_cols = 5;
_rows = 10;
constructor() { }
ngOnInit() {
}
get cols() {
return Array(this._cols).fill(null).map((el, index) => index);
}
get rows() {
return Array(this._rows).fill(null).map((el, index) => index);
}
In html:
<div class="charts-setup">
<div class="col" *ngFor="let col of cols; let colIdx = index">
<div class="row" *ngFor="let row of rows; let rowIdx = index">
Col: {{colIdx}}, row: {{rowIdx}}
</div>
</div>
</div>
Solution 17:[17]
Here is something quite clean and simple for Angular:
In .ts:
max = 10;
In .html:
<div *ngFor="let dummy of ','.repeat(max).split(','); index as ix">
- {{ix + 1}}:
</div>
Solution 18:[18]
I think the simple and short solution is here..
Your my.component.ts file
setArrayFromNumber(i: number) {
return new Array(i);
}
Your my.component.html file
<li *ngFor='let in of setArrayFromNumber(5); let i = index'>{{ i }}</li>
That's it!!
Sources
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