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Front-End Development Projects with Vue.js

By Raymond Camden , Hugo Di Francesco , Clifford Gurney and 2 more
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  1. Free Chapter
    2. Working with Data
About this book
Are you looking to use Vue 2 for web applications, but don't know where to begin? Front-End Development Projects with Vue.js will help build your development toolkit and get ready to tackle real-world web projects. You'll get to grips with the core concepts of this JavaScript framework with practical examples and activities. Through the use-cases in this book, you'll discover how to handle data in Vue components, define communication interfaces between components, and handle static and dynamic routing to control application flow. You'll get to grips with Vue CLI and Vue DevTools, and learn how to handle transition and animation effects to create an engaging user experience. In chapters on testing and deploying to the web, you'll gain the skills to start working like an experienced Vue developer and build professional apps that can be used by other people. You'll work on realistic projects that are presented as bitesize exercises and activities, allowing you to challenge yourself in an enjoyable and attainable way. These mini projects include a chat interface, a shopping cart and price calculator, a to-do app, and a profile card generator for storing contact details. By the end of this book, you'll have the confidence to handle any web development project and tackle real-world front-end development problems.
Publication date:
November 2020
Publisher
Packt
Pages
774
ISBN
9781838984823

 

2. Working with Data

Overview

In this chapter, you will expand on what you learned in the previous chapter by introducing more ways to control data inside Vue components. You will learn how to set up advanced watchers to observe data changes inside your components, and utilize Vue's powerful reactive data feature, computed data properties, to concisely output just the data you need in your template. You will also be able to utilize asynchronous methods to fetch data for your Vue components.

By the end of this chapter, you will be able to watch, manage, and manipulate data from various sources in your Vue.js components.

 

Introduction

In the previous chapter, you were introduced to the concepts of single-file components and the Vue API, which provides access to methods, directives, and data properties. Building on these foundations, we will be introducing computed properties, which, like data properties, are reactive in the UI but can perform powerful calculations, and their results are cacheable, increasing the performance of your project. When building e-commerce stores, you will usually want to calculate pricing and cart items reactively as users interact with your UI, which in the past would need to be achieved without a page reload using something like jQuery. Vue.js makes short work of these common frontend tasks by introducing computed properties that react immediately to frontend user input.

Let's begin by introducing reactive data that can be computed on the fly and understanding how to call and manipulate asynchronous data.

 

Computed Properties

Computed properties are a unique data type that will reactively update when source data used within the property is updated. They may look like a Vue method, but they are not. In Vue, we can track changes to a data property by defining them as a computed property, add custom logic within this property, and use it anywhere within the component to return a value. Computed properties are cached by Vue, making them more performant for returning data than a data prop or using a Vue method.

Instances where you may use a computed property include but are not limited to:

  • Form validation:

    In this example, an error message will appear when the total data property is less than 1. The computed property for total will update every time a new piece of data is added to the items array:

    <template>
        <div>{{errorMessage}}</div>
    </template>
    <script>
        export default {
         ...
 

Computed Setters

In the last exercise, you saw how to write maintainable and declarative computed properties that are reusable and reactive and can be called anywhere within your component. In some real-world cases when a computed property is called, you may need to call an external API to correspond with that UI interaction or mutate data elsewhere in the project. The thing that performs this function is called a setter.

Computed setters are demonstrated in the following example:

data() {
  return {
    count: 0
  }
},
computed: {
    myComputedDataProp: {
      // getter
      get() {
        return this.count + 1
      },
      // setter
      set(val) {
        this.count = val - 1
 ...
 

Watchers

Vue watchers programmatically observe component data and run whenever a particular property changes. Watched data can contain two arguments: oldVal and newVal. This can help you when writing expressions to compare data before writing or binding new values. Watchers can observe objects as well as string, number, and array types. When observing objects, it will only trigger the handler if the whole object changes.

In Chapter 1, Starting Your First Vue Project, we introduced life cycle hooks that run at specific times during a component's lifespan. If the immediate key is set to true on a watcher, then when this component initializes it will run this watcher on creation. You can watch all keys inside of any given object by including the key and value deep: true (default is false) To clean up your watcher code, you can assign a handler argument to a defined Vue method, which is best practice for large projects.

Watchers complement the usage of computed data since they...

 

Deep Watching Concepts

When using Vue.js to watch a data property, you can purposefully observe keys inside an object for changes, rather than changes to the object itself. This is done by setting the optional deep property to true:

data() {
  return {
      organization: {
        name: 'ABC',
        employees: [
            'Jack', 'Jill'
        ]
      }
  }
},
watch: {
    organization: {
      handler: function(v) {
        this.sendIntercomData()
      },
      deep: true,
      immediate: true,
  &...
 

Methods versus Watchers versus Computed Props

In the Vue.js toolbox, we have access to methods, watchers, and computed properties. When should you use one or the other?

Methods are best used to react to an event occurring in the DOM, and in situations where you would need to call a function or perform a call instead of reference a value, for example, date.now().

In Vue, you would compose an action denoted by @click, and reference a method:

<template>
    <button @click="getDate">Click me</button>
</template>
<script>
export default {
    methods: {
        getDate() {
            alert(date.now())
        }
    }
}
</script>

Computed props are best used when reacting to data updates or for composing complicated expressions for us...

 

Async Methods and Data Fetching

Asynchronous functions in JavaScript are defined by the async function syntax and return an AsyncFunction object. These functions operate asynchronously via the event loop, using an implicit promise, which is an object that may return a result in the future. Vue.js uses this JavaScript behavior to allow you to declare asynchronous blocks of code inside methods by including the async keyword in front of a method. You can then chain then() and catch() functions or try the {} syntax inside these Vue methods and return the results.

Axios is a popular JavaScript library that allows you to make external requests for data using Node.js. It has wide browser support making it a versatile library when doing HTTP or API requests. We will be using this library in the next exercise.

Exercise 2.06: Using Asynchronous Methods to Retrieve Data from an API

In this exercise, you will asynchronously fetch data from an external API source and display it in the...

 

Summary

In this chapter, you were introduced to Vue.js computed and watch properties, which allow you to observe and control reactive data. You also saw how to use methods to asynchronously fetch data from an API using the axios library and how to flatten the data to be more usable within the Vue template using computed props. The differences between using methods and computed and watch properties were demonstrated by building search functionality using each method.

The next chapter will cover the Vue CLI and show you how to manage and debug your Vue.js applications that use these computed properties and events.

About the Authors
  • Raymond Camden

    Raymond Camden is a developer advocate for IBM. His work focuses on the MobileFirst platform, Bluemix, hybrid mobile development, Node.js, HTML5, and web standards in general. He is a published author and presents at conferences and user groups on a variety of topics. Raymond can be reached at his blog, on Twitter, or via email. He is the author of many development books, including Apache Cordova in Action and Client-Side Data Storage.

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  • Hugo Di Francesco

    Hugo Di Francesco is a software engineer who has worked extensively with JavaScript. He holds a MEng degree in mathematical computation from University College London (UCL). He has used JavaScript across the stack to create scalable and performant platforms at companies such as Canon and Elsevier. He is currently tackling problems in the retail operations space with Node.js, React, and Kubernetes while running the eponymous Code with Hugo website. Outside of work, he is an international fencer, in the pursuit of which he trains and competes across the globe.

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  • Clifford Gurney

    Clifford Gurney is a solution-focused and results-oriented technical lead at a series-A funded startup. A background in communication design and broad exposure to leading digital transformation initiatives enriches his delivery of conceptually designed front-end solutions using Vue JS. Cliff has presented at the Vue JS Melbourne meetups and collaborates with other like-minded individuals to deliver best in class digital experience platforms.

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  • Philip Kirkbride

    Philip Kirkbride has over 5 years of experience with JavaScript and is based in Montreal. He graduated from a technical college in 2011 and since then he has been working with web technologies in various roles.

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  • Maya Shavin

    Maya is Senior Software Engineer in Microsoft, working extensively with JavaScript and frontend frameworks and based in Israel. She holds a B.Sc in Computer Sciences, B.A in Business Management, and an International MBA from University of Bar-Ilan, Israel. She has worked with JavaScript and latest frontend frameworks such as React, Vue.js, etc to create scalable and performant front-end solutions at companies such as Cooladata and Cloudinary, and currently Microsoft. She founded and is currently the organizer of the VueJS Israel Meetup Community, helping to create a strong playground for Vue.js lovers and like-minded developers. Maya is also a published author, international speaker and an open-source library maintainer of frontend and web projects.

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