如何使用ngFor指令获取angular 5中的第一个元素？

Question

ngFor directive worked fine when I used to show all the colors from an array of colors but when I tried to check whether it is first element of the array or not then it shows an error "can't bind to ngForFirst since it is not .... blah blah blah ". It shows almost a page full of error. I'm very new to angular and the tutorial I'm going through the tutor doesn't get any error. Don't know why. Help me

    import { Component, OnInit } from '@angular/core';

    @Component({
     selector: 'app-test',
     template: `
       <div *ngFor = "let color of colors; first as i">
           <h3> {{i}}  </h3>
       </div>` ,
     styles: []
    })

    export class TestComponent implements OnInit {
      public name = "Dipesh";
      public colors = ["Red", "Black", "Green"];
      constructor() { }

      ngOnInit() {
      }

      }

Answer 1

Try this

 <div *ngFor = "let color of colors; let first = first; let last = last">
               <h3> {{first}}  </h3>
               <h3> {{last}}  </h3>
 </div>

Answer 2

You can access to the first element like this:

<div *ngFor="let color of colors; let first = first;"> ...

Note:

You have more functionallity available like: odd , even or last

Official documentation here

Answer 3

with using "as" you try to translate " first " into " i " type object. that is why you are getting error.

you can declare variable in angular by using "let" keyword. ex : let variableName = index