Unexpected glitch when assigning arrays in Angular 2+?

I have a simple question that has been puzzling me. When attempting to reassign an element of an array of objects to another object that meets specific criteria, I noticed that nothing happens. However, if I first set the element to null and then reassign it, the operation works successfully. Below is the list of objects being used:

servers = [
{
  instanceType: 'medium',
  name: 'Production',
  status: 'stable',
  started: new Date(15, 1, 2017)
},
{
  instanceType: 'large',
  name: 'User Database',
  status: 'stable',
  started: new Date(15, 1, 2017)
},
{
  instanceType: 'small',
  name: 'Development Server',
  status: 'offline',
  started: new Date(15, 1, 2017)
},
{
  instanceType: 'small',
  name: 'Testing Environment Server',
  status: 'stable',
  started: new Date(15, 1, 2017)
}

];

Here is the method that does not yield results:

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
  name: 'sort'
})
export class SortPipe implements PipeTransform {

  transform(value: any, args?: any): any {
    for (const i of value) {
      for (const j of value.slice(value.indexOf(i) + 1)) {
        if (i.name > j.name) {
          value[value.indexOf(i)] = j;
          value[value.indexOf(j)] = i;
        }
      }
    }
    return value;
  }

}

And here is the working method:

import { Pipe, PipeTransform } from '@angular/core';
@Pipe({
  name: 'sort'
})
export class SortPipe implements PipeTransform {

  transform(value: any, args?: any): any {
    for (const i of value) {
      for (const j of value.slice(value.indexOf(i) + 1)) {
        if (i.name > j.name) {
          const index1 = value.indexOf(i);
          const index2 = value.indexOf(j);
          value[index1] = null;
          value[index2] = null;
          value[index1] = j;
          value[index2] = i;
        }
      }
    }
    return value;
  }

}

It's not a critical issue, but I am now curious about why one method fails while the other succeeds. Thank you for your time!

EDIT 1: Modified (i.name[0] > j.name[0]) to (i.name > j.name) for consistency. Both checks produced identical outcomes.

Answer №1

When you're working with traditional for loops, the index i.name[0] is typically used. For example:

(for(var i=0; i > length; i++)
.

On the other hand, when using the for (const i of value) method, the value is readily available when you call i.

Answer №2

When carrying out this action

      value[value.indexOf(i)] = j;
      value[value.indexOf(j)] = i;

The second line, value.indexOf(j), essentially gives back the previous position of i since you have already replaced it with j. Consequently, you end up with

      value[value.indexOf(i)] = i;

which doesn't change anything.

If you require both array values and their respective indexes when iterating, consider using

 for (let [index, value] of array.entries())

instead of just using for..of

Furthermore, if your goal is simply to sort your servers array by name, a more straightforward approach would be:

 value.sort((x, y) => x.name.localeCompare(y.name))

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