[angular] 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>

?

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);
    }
  }
}

http://plnkr.co/edit/bzoNuL7w5Ub0H5MdYyFR?p=preview

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>

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>

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).

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);

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);
  }
}

Working Demo

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);
  }
}

#Working demo

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>

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>

@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.

<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.

Using custom Structural Directive with index:

According Angular documentation:

createEmbeddedView Instantiates 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));
  }
}

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.

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