Last time (in part 1 of this series) we figured out how to add Vue to our index.html with a regular <script> tag, and we managed to add our very first reactive property to the page. Today, let's learn how we can change this property with user input.
Our code so far looks like this:
<html>
<head>
<title>Vue 101</title>
</head>
<body>
<h1>Hello!</h1>
<div id="app">
<p>My local property: {{ myLocalProperty }}</p>
</div>
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<script>
const app = new Vue({
el: '#app',
data: {
myLocalProperty: 'Im a local property value'
}
});
</script>
</body>
</html>
Listening to user events
In order to better showcase the reactivity of Vue, and to learn how to react to user events we are going to add a button to our app that will change the value of our myLocalProperty prop.
Go ahead and first add a new button to our <div id="app">.
<div id="app">
<p>My local property: {{ myLocalProperty }}</p>
<hr>
<button>Click me</button>
</div>
Now, how do we react to this button getting clicked?
If you come from a jQuery background your instinct may be to try to do something like this: $('button').click();, however, there's a golden rule in Vue. NEVER manipulate the DOM (elements in the page's HTML) directly.
Without going into super intricate details, Vue keeps a virtual "copy" of your HTML (in this case our div with the "app" ID) and automagically 🧙♀️ 🧙♂️ figures out where and how to update it when properties change.
If you make changes to the DOM directly with JavaScript, you risk losing these changes and unexpected behavior whenever Vue re-renders the content, because it will not be aware of these changes.
Enough theory though, let's move on with the clicking. Add this event handler to our button:
<button v-on:click="myLocalProperty = 'The button has been clicked'">
Click me
</button>
A couple of things are happening here.
v-on:click="" In Vue we have these "directives" that we can add to our HTML content.
A directive simply put is an HTML parameter that Vue can understand.
In this particular case, we are telling Vue: Vue (v-), on the user's click do this: "myLocalProperty = 'The button has been clicked'", which is simply an inline declaration to change the value of our property.
If you go ahead and open your index.html file now in the browser and click the button, you will see the string that we interpolated earlier inside the {{ }} in our code will react to our button modifying the property.
Alternate syntax
In most places you will most likely not find events being set on the HTML with v-on:[eventname] as we have in this example because in Vue we have a very handy shorthand for this type of thing. @[eventname].
Let's change our <button> click even to to use this shorthand:
<button @click="myLocalProperty = 'The button has been clicked'">Click me</button>
Methods
In most cases, when a user event like the click of a button is fired, you will need to do a lot more than changing the value of a variable. So let's learn about methods (aka, functions).
To continue with our example, let's make the button call a function that will do something really simple, it'll change the value of myLocalProperty by appending a random number to a string.
Delete our previous implementation of @click and replace it with this:
<button @click="buttonClicked">Click me</button>
Notice that we're not adding a () after "buttonClicked". We can omit these when we are not passing any arguments to our function. For example, @click="changeName('Marina')". (More on this later when we look at conditional rendering 🙂)
Now that we have our button ready to execute buttonClicked on clicks, we need to actually write this function.
Vue has a special place to write functions that our Vue instance can use. This place is inside the { } we passed to our new Vue({}) line before.
We will create a methods: {} property that will hold an object filled with our functions.
<script>
const app = new Vue({
el: '#app',
data: {
myLocalProperty: 'Im a local property value'
},
methods: { // 1
buttonClicked() { // 2
const newText = 'The new value is: ' + Math.floor( Math.random() * 100); // 3
this.myLocalProperty = newText; // 4
}
}
});
</script>
Let's dissect this:
- We declare the
methodsproperty inside our Vue instance. As I mentioned, in here you will put all your instance methods/functions. - Inside the
methodsobject{ }we declarebuttonClicked(), which is the function we are trying to call on our@clicklistener. We're not going to use any parameters at this point so empty(). - We join the value of the rounded down value
Math.floorof the result of multiplying the random value of 0-1 by 100 to a string and store it in a constant. - We assign the value of our new string to
myLocalProperty. Now be very careful about this tiny detail 🙃 (lame pun intended). When we assign new values to the properties inside the instance'sdataproperty (the one insidedata: {}) you MUST access it throughthis.[prop-name].
In the context of a method the keyword this refers to the Vue instance. Vue will perform some magic behind the scenes so that you can read/write to your properties inside data by doing this.property = value.
Now that we have everything set up, reload your index.html file and click on your button. The value of our interpolated {{ }} string on the containing <p> will be updated every time you click the button, for every single time the buttonClicked function is executed. Once again, the magic of Vue's reactivity is coming into play.
Wrapping up
If at this point you're thinking, well, this is really easy then you're on the right track. One of the things I love the most about this framework is its clear syntax and simplicity. It just works. But this should not be confused with thinking that Vue is not powerful.
We're merely scratching the surface of what we can do with Vue so far, but you'll see as we progress through these articles that these tiny building blocks put together will soon make the core of your amazing next app.
Stay tuned for part 3!
Top comments (25)
Really like it, I hope you will go through the full Vue features because if all is explained with the same quality that will be by far the best tutorial to Vue.
Hi Fred, thanks for your kind words. That's the plan, to do a weekly release and walk through every feature!
Thank you, this helped me better understand a Vue app I cobbled together from examples! Really appreciate the clear explanation and dissection.
And, more excitingly, within minutes of reading this I was able to refactor the previously mentioned app to use a click event to call the method with an API call, replacing the window.location.reload(true) full page reload. Thanks again ⚡️👍🏼
Awesome Dana!!! Next week ill go into conditional rendering so stay tuned :)
Thank you so much for this acticle. Would be nice if you create tutorial that show how to use Django Rest Framework with Vue.js. I mean registration with confirmation an email, login, change a pass, login with Facebook, Google etc...
Thank you very much for taking the effort to teach. These tutorials are amazing compared to video lectures. Learning from text tutorials is helping a lot. I hope you will take us to the core of Vue with the same(or >=) passion.
another great work.. waiting for more..👏👏👏
Thanks Jonathan! Comments like these keep me motivated :)
Great also waiting for more. Thx
Thanks!
Explanation on point, helped me understanding the basics better.
Thanks for your feedback :)
Wow awesome article, makes me wanna do something with Vue again 😊
Do eeeeet! :D
I like the articles on Vue that you have posted. Great tutorials parts. I am learning Vue and doing POC'S on it.
If possible can you post any articles on Vuex and Vue-Router with Vue.
Hey Surya, thanks for you words :) Keep posted on my twitter account @marinamosti , I post new articles there and will have a Vuex series up soon I hope!
Thank you :)
Nice follow up on the first tutorial. I like the explanations of what Vue is doing behind the scenes.
Thanks for the tutorial! Very well done!
Thanks Nicolas, glad you enjoyed it :)
Keep up Marina. well, this is really easy
Wow awesome article keep it continue
Thanks!
Is it possible in Vue.js to put event handling code just in one place(in js file), like we do in jquery.
$("#btnSubmit").click(function(e){
alert("example");
});
Hi Aniketnaik, well... In Vue as you probably know by now, we declare the listeners directly on the template using @click or @event and pass in the name of a method. It is possible to attach listeners using vanilla javascript by doing element.addEventListener and passing a function, but it depends on what you're trying to accomplish. Good luck