Mastering AngularJS ng-repeat Directive: The Ultimate Guide to Repeating Elements in Your Web Application

Are you tired of manually creating HTML elements to display repetitive data on your web application? AngularJS ng-repeat directive is here to rescue you! ng-repeat is a powerful and flexible way to display repeated elements in your web application.

In this ultimate guide, we will dive deep into ng-repeat, its syntax, and how to use it to display arrays, objects, and dynamic lists. We will also explore advanced directives, filters, and common errors associated with ng-repeat.

By the end of this article, you will have mastered AngularJS ng-repeat directive and be able to create dynamic and visually appealing web applications that will impress your users.

Understanding the Syntax of ng-repeat

Before we dive into how to use ng-repeat, let’s first understand its syntax. ng-repeat is an AngularJS directive that takes an array or an object and repeats a section of HTML code for each element in the array or object.

The basic syntax for ng-repeat is:

html div ng-repeat="item in items"> {{ item }} /div>

In the above code, we are repeating the div> element for each item in the items array. The item variable is created by ng-repeat and represents the current item in the array.

We can also use the $index variable, which represents the current index of the repeated element in the array. The syntax for using $index is:

html div ng-repeat="item in items"> {{ $index + 1 }} - {{ item }} /div>

In the above code, we are displaying the index of each element in the array along with its value.

Repeating Arrays with ng-repeat

The most common use case for ng-repeat is to repeat HTML elements for each item in an array. Let’s take a look at an example:

html ul> li ng-repeat="fruit in fruits">{{ fruit }}/li> /ul>

In the above code, we are repeating the li> element for each fruit in the fruits array. The output will be an unordered list of fruits.

We can also use ng-repeat to repeat a section of HTML code multiple times based on the length of an array. For example:

html div ng-repeat="n in [1,2,3]"> {{ n }} /div>

In the above code, we are repeating the div> element three times, once for each element in the array.

Repeating Objects with ng-repeat

In addition to arrays, we can also use ng-repeat to repeat HTML elements for each key-value pair in an object. Let’s take a look at an example:

html ul> li ng-repeat="(key, value) in person">{{ key }}: {{ value }}/li> /ul>

In the above code, we are repeating the li> element for each key-value pair in the person object. The output will be an unordered list of person’s attributes.

Using Filters with ng-repeat

Filters are a powerful tool in AngularJS that allow us to format data before it is displayed to the user. We can use filters with ng-repeat to manipulate the data before it is repeated.

Let’s take a look at an example:

html ul> li ng-repeat="fruit in fruits | orderBy:'name'">{{ fruit.name }}/li> /ul>

In the above code, we are using the orderBy filter to sort the fruits array by the name property before repeating the li> element.

We can also use other filters like limitTo, uppercase, lowercase, and date to format the data before it is displayed.

Advanced Directives with ng-repeat

In addition to the basic syntax, ng-repeat also supports advanced directives that allow us to customize the repeated elements.

track by

The track by directive allows us to specify a unique identifier for each repeated element. This is useful when we need to update the repeated elements dynamically.

html ul> li ng-repeat="fruit in fruits track by $index">{{ fruit }}/li> /ul>

In the above code, we are using the $index variable as the unique identifier for each fruit.

ng-repeat-start and ng-repeat-end

The ng-repeat-start and ng-repeat-end directives allow us to repeat a section of HTML code that includes multiple elements.

html div ng-repeat="fruit in fruits"> h3 ng-repeat-start="">{‌{ fruit.name }}/h3> p>{‌{ fruit.description }}/p> hr ng-repeat-end> /div>

In the above code, we are repeating the h3>, p>, and hr> elements for each fruit in the fruits array.

Creating Dynamic Lists with ng-repeat

One of the powerful features of ng-repeat is the ability to create dynamic lists. Let’s take a look at an example:

html ul> li ng-repeat="fruit in fruits" ng-class="{ 'highlight': fruit.quantity 10 }"> {{ fruit.name }} - {{ fruit.quantity }} /li> /ul>

In the above code, we are using the ng-class directive to highlight the list item if the quantity of the fruit is less than 10.

We can also use other directives like ng-show, ng-hide, and ng-if to create dynamic lists based on different conditions.

Examples of ng-repeat in Action

Now that we have covered the basics of ng-repeat, let’s take a look at some examples of ng-repeat in action.

Example 1: Repeat an Array

html ul> li ng-repeat="fruit in ['Apple', 'Banana', 'Orange']">{{ fruit }}/li> /ul>

Example 2: Repeat an Object

html ul> li ng-repeat="(key, value) in { 'name': 'John', 'age': 30, 'gender': 'male' }">{{ key }}: {{ value }}/li> /ul>

Example 3: Create a Dynamic List

html ul> li ng-repeat="fruit in fruits" ng-class="{ 'highlight': fruit.quantity 10 }"> {{ fruit.name }} - {{ fruit.quantity }} /li> /ul>

Common Errors with ng-repeat and How to Troubleshoot Them

ng-repeat is a powerful directive, but it can also be a source of errors if not used correctly. Here are some common errors with ng-repeat and how to troubleshoot them:

1. Error: ngRepeat:dupes

This error occurs when there are duplicate items in the array or object being repeated. To fix this error, ensure that each item in the array or object is unique.

2. Error: $digest already in progress

This error occurs when there is a circular dependency in the data being repeated. To fix this error, ensure that there are no circular dependencies in the data.

3. Error: ngRepeat:badident

This error occurs when the ng-repeat expression is invalid. To fix this error, ensure that the ng-repeat expression is valid and follows the correct syntax.

Conclusion and Final Thoughts

In conclusion, AngularJS ng-repeat directive is a powerful and flexible way to display repeated elements in your web application. By mastering ng-repeat, you will be able to create dynamic and visually appealing web applications that will impress your users.

We have covered the basics of ng-repeat, including its syntax, how to repeat arrays and objects, using filters, advanced directives, creating dynamic lists, and troubleshooting common errors.

With this ultimate guide, you are now equipped with the knowledge to take your web development skills to the next level. So, what are you waiting for? Go ahead and master AngularJS ng-repeat directive today!