Auto-Scroll-To Directive

While working on one of my recent projects I encountered a situation where I had to scroll to a particular element on a page. This was easily achieved using the $anchorScroll service in angularJS. It simply checks the current value of $location.hash() and scrolls to the related element.

You must be thinking what exactly is $anchorScroll? What is $location.hash()? How does $anchorScroll works?

Let's go ahead:

$location is a service in angularJS which exposes the current URL in the address bar so that it can be observed or manipulated. It represents the URL object as set of methods protocol, host, port, path, search, hash.

hash() method sets/returns the anchor part of the URL. Anchor basically refers to internal section of the web document.

$anchorScroll watches $location.hash() and automatically scrolls to match any anchor whenever it changes.

It's time for some action now. Have a look at the piece of HTML given below:

<!DOCTYPE html>
<html ng-app="myApp">
<head lang="en">
    <meta charset="UTF-8">
    <title>My Page</title>
</head>
<body>
<div id="FirstDiv">
    <h1>Section 1</h1>
    <br>
    <br>
    <br>
    <br>
    <br>
    <br>
</div>
<div id="SecondDiv">
    <h1>Section 2</h1>
    <br>
    <br>
    <br>
    <br>
    <br>
    <br>
</div>
<div id="ThirdDiv">
    <h1>Section 3</h1>
    <br>
    <br>
    <br>
    <br>
    <br>
    <br>
</div>
<div id="FourthDiv">
    <h1>Section 4</h1>
    <br>
    <br>
    <br>
    <br>
    <br>
    <br>
</div>
<div id="FifthDiv" auto-scroll-to="FifthDiv">
    <h1>Section 5</h1>
    <br>
    <br>
    <br>
    <br>
    <br>
    <br>
</div>
<div id="SixthDiv">
    <h1>Section 6</h1>
    <br>
    <br>
    <br>
    <br>
    <br>
    <br>
</div>
<div id="SeventhDiv">
    <h1>Section 7</h1>
    <br>
    <br>
    <br>
    <br>
    <br>
    <br>
</div>
<div id="EighthDiv">
    <h1>Section 8</h1>
    <br>
    <br>
    <br>
    <br>
    <br>
    <br>
</div>
<script src="angular.min.js"></script>
<script src="autoScrollTo.js"></script>
</body>
</html>

Now, suppose we want that every time we land to the 'myPage.html', it should automatically scroll to section 5 of the page. As explained above, this can be easily achieved using the anchorScroll() service of Angular. But what if tomorrow same requirement comes up for some other web page. Since scrolling to a particular section on a page is a very common use case, therefore I thought of making a directive so that it can be used wherever and whenever required.

Here we go:

(function (ng) {
    'use strict';
    var app = ng.module('myApp', []);
    app.directive('autoScrollTo', ['$location', '$anchorScroll', '$timeout', function ($location, $anchorScroll, $timeout) {
        return {
            restrict: 'A',
            scope: false,
            link: function (scope, elem, attr) {
                //code to scroll on the basis of provided id
                $timeout(function () {
                    $location.hash(attr.autoScrollTo);
                    $anchorScroll();
                });
            }
        }
    }]);
}(angular));

In the above JavaScript snippet we have basically done the following:

  1. Defined a directive named as autoScrollTo.
  2. While declaring the directive, we have also declared the dependencies : $location , $timeout and $anchorScroll.
  3. We would be using this directive as an attribute of the element, hence we have given restrict property as A. In case you want to have deeper understanding on how to make custom directives, please have a look at this very informative blog by Amit Thakkar.
  4. Then, there is a link function which is executed while attaching the template to the DOM. Link function basically has parameters:
    1. scope - angular scope object
    2. element - jqLite-wrapped element that this directive matches
    3. attribute - hash object with key-value pairs of normalized attribute names and their corresponding attribute values
  5. We have placed our code for scrolling into a self executing function and we have applied a delay using $timeout.

    You must be thinking that we have forgotten to specify the time of delay. Well, we have deliberately not mentioned the delay time as omitting the delay time defaults it to 0. But the code block contained in it is executed only after DOM has been manipulated by Angular and after the browser renders.

  6. Then we have used $location.hash() to specify the element to which we need to automatically scroll. We know that attribute would give us the value of the corresponding attribute, so we are finding here the value of the autoScrollTo attribute which was placed in the div with id FifthDiv.
  7. And then, off course in the end we have used our $anchorScroll() service to scroll to the part of the page, defined through $location.hash() method.

Your autoScrollTo directive is now ready to use anywhere!

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