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AngularJS ngRepeat and Tracking

ngRepeat creates a view for each collection item. Track changing records by a stable unique key so their views remain attached to the same records during reordering.

How it works

The desk can reverse its repair queue. Each editable note belongs to a request ID rather than an array position. Tracking by $index can be reasonable for a truly fixed list, but it can attach local DOM state to the wrong record when a changing list is reordered. Avoid duplicate identifiers and avoid generating fresh random keys during evaluation.

Run the code

AngularJS 1.8.3 is a legacy framework whose official support ended in January 2022. These examples teach maintenance, not a recommendation for a new application. They need a separate local browser page; Bhylu has no AngularJS playground.

In an empty folder save the HTML below as lists.html and the server as lab-server.mjs. Make a vendor folder and save the four pinned libraries there, retaining their MIT notices. With Node 22 or later run node lab-server.mjs lists.html, then open http://127.0.0.1:8136/. Stop that lab before running a different lesson. The server supplies fixed read-only HTTP fixtures; no data is saved and it does not connect to SQL. No PHP, Apache or MySQL configuration changes are needed.

Example

lists.html

<!doctype html>
<html lang="en" ng-app="repairLab" ng-strict-di>
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width,initial-scale=1" />
    <title>AngularJS ngRepeat and Tracking</title>
    <style>
      :root {
        font:
          18px/1.55 system-ui,
          sans-serif;
        color: #0f3464;
        background: #fff;
        color-scheme: light;
      }
      * {
        box-sizing: border-box;
      }
      body {
        margin: 0;
      }
      main {
        max-width: 50rem;
        margin: auto;
        padding: 1.2rem;
      }
      h1 {
        font-size: 1.65rem;
      }
      label {
        display: block;
        margin: 0.6rem 0;
      }
      input,
      select,
      textarea,
      button {
        font: inherit;
        max-width: 100%;
        padding: 0.35rem;
        margin: 0.2rem;
      }
      button {
        border: 1px solid #034fa0;
        border-radius: 0.25rem;
        background: #034fa0;
        color: white;
      }
      button:disabled {
        opacity: 0.55;
      }
      output,
      [role="status"] {
        display: block;
        min-height: 1.5rem;
      }
      table {
        border-collapse: collapse;
        width: 100%;
      }
      td,
      th {
        padding: 0.4rem;
        border: 1px solid #a5bbd4;
        text-align: left;
      }
      pre {
        white-space: pre-wrap;
        overflow-wrap: anywhere;
      }
      :focus-visible {
        outline: 3px solid #0078d4;
        outline-offset: 3px;
      }
      [ng-cloak] {
        display: none !important;
      }
      .marked {
        font-weight: 700;
      }
      .error {
        color: #a02424;
      }
      :root[data-theme="dark"] {
        color: #d6e7fb;
        background: #061d30;
        color-scheme: dark;
      }
      :root[data-theme="dark"] .error {
        color: #ffb4b4;
      }
    </style>
  </head>
  <body>
    <main ng-controller="DeskController as vm" ng-cloak>
      <h1>Community repair desk</h1>
      <p>AngularJS 1.8.3 · Legacy maintenance lab · Local demonstration</p>
      <button type="button" ng-click="vm.reverse()">Reverse queue</button>
      <ul>
        <li
          ng-repeat="item in vm.items track by item.id"
          data-id="{{ item.id }}"
        >
          <label>{{ item.name }}<input value="{{ item.name }}" /></label>
        </li>
      </ul>
      <p data-result>{{ vm.items.length }} requests</p>
    </main>
    <script src="/vendor/angular.min.js"></script>
    <script>
      (function () {
        "use strict";
        var app = angular.module("repairLab", []);
        app.controller("DeskController", [
          function () {
            var vm = this;
            vm.items = [
              { id: "RQ-4", name: "Hinge" },
              { id: "RQ-8", name: "Latch" },
            ];
            vm.reverse = function () {
              vm.items = vm.items.slice().reverse();
            };
          },
        ]);
      })();
    </script>
  </body>
</html>
Focus on the bindings and controller

This excerpt leaves out the document shell, styles and library files. Use the complete download to run it.


<button type="button" ng-click="vm.reverse()">Reverse queue</button>
<ul>
  <li ng-repeat="item in vm.items track by item.id" data-id="{{ item.id }}">
    <label>{{ item.name }}<input value="{{ item.name }}" /></label>
  </li>
</ul>
<p data-result>{{ vm.items.length }} requests</p>
<script>
  (function () {
    "use strict";
    var app = angular.module("repairLab", []);
    app.controller("DeskController", [
      function () {
        var vm = this;
        vm.items = [
          { id: "RQ-4", name: "Hinge" },
          { id: "RQ-8", name: "Latch" },
        ];
        vm.reverse = function () {
          vm.items = vm.items.slice().reverse();
        };
      },
    ]);
  })();
</script>

Expected result

2 requests

The browser review edits the hinge input, reverses the queue and confirms the same input node and edited value survive. That tests identity instead of merely counting rows. A real editor would usually bind its note to a model; the deliberately unbound input makes DOM identity visible here.

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