Referring to properties passes as props in Vue.js components - vue.js

I've started working on a board game prototype and decided to go with Vue.js. I have some experience with JavaScript and everything was going fine ... until I tried to access a property passed with 'props' in a component.
Here's the whole code:
<!DOCTYPE HTML>
<html>
<head>
<title>Board</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<style type="text/css">
#board {
width: 600px;
}
.square { width: 100px; height: 100px; margin: 1px; border: 1px solid grey; display: inline-block; float: left; }
</style>
</head>
<body>
<div id="board">
<square v-for="square in squares"></square>
</div>
<script>
var app = new Vue({
el: '#board',
data: {
squares: []
}
})
const rows = 5
const cols = 5
const reservedLocation = { row: 2, col: 2 }
Vue.component('square', {
props: [
'row',
'col',
'type',
],
template: '<div class="square" v-on:click="logLocation"></div>',
methods: {
logLocation: function() {
console.log(this)
console.log("Location: " + this.col + "x" + this.row )
},
},
})
for (var row=0; row<rows; row++) {
for (var col=0; col<cols; col++) {
const type = (row == reservedLocation.row && col == reservedLocation.col) ? 'reserved' : 'empty'
app.squares.push({ row: row, col: col, type: type })
}
}
</script>
</body>
</html>
What's happening there is the "board" div is filled with the "square" components. Each square component has the 'row', 'col' and 'type' properties, passed to it as 'props'. When the user click on a square, the 'logLocation' function of the corresponding component is called and all that function does is, it logs the 'row' and 'col' properties.
Everything works fine except the message logged is: "Location: undefinedxundefined", in other words, both this.col and this.row seems to be undefined. I've checked 'this', and it seems to be the correct component.
I'm sure it's something obvious but I couldn't find an answer in either the official documentation, in tutorials or even here, on Stack Overflow itself – perhaps I'm not using the correct terms.
A bit of new info: the 'row' and 'col' properties are set on the component object and in the '$props' property but the value they return in 'undefined'. Am I, somehow, passing the parameters incorrectly?
Solution
Turns out, there is a section in the Vue.js documentation dedicated specifically to using 'v-for' with components: "v-for with a Component" and here's the relevant portion of the code:
<div id="board">
<square
v-for="square in squares"
:key="square.id"
:row="square.row"
:col="square.col"
:type="square.type"
></square>
</div>
Huge thanks to Stephen Thomas for pointing me in the right direction!


You've defined the props correctly, and you're accessing the props correctly, but you haven't actually set them to any value. The markup:
<square v-for="square in squares"></square>
doesn't pass the props to the component. Perhaps you want something like
<div v-for="row in rows" :key="row">
<div v-for="col in cols" :key="col">
<square :row="row" :col="col"></square>
</div>
</div>


Try to use
console.log("Location: " + this.$props.col + " x " + this.$props.row )

Related

Trouble with Vue methods

doing some Vue.js challenges for school and having trouble with a function that should trigger on a hover.
I need the div with the class 'redBox' to grow 10 pixels taller each time it is hovered over.
Here's my code:
<html>
<head>
<title>v-on Event Handlers</title>
<meta charset="UTF-8">
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<style>
.box{width:200px; height:200px; background:green; border:2px solid black; text-align:center; line-height:200px; color:white;}
.hidden{display:none;}
.redBox{width: 100px; height: 100px; background-color: red; margin: 2em;}
</style>
</head>
<body>
<div id="app">
<div v-bind:class="{box:true, hidden:boxHidden}">{{message}}</div>
<button v-on:click="showhide();">{{buttonText}}</button>
<div class="redBox" v-on:hover="hoverGrow();"></div>
</div>
<script>
var app = new Vue({
el: '#app',
data:{
boxHeight:200,
boxHidden : false,
message : 'Make me disappear!',
buttonText : "Hide",
hovered: false,
},
methods:{
showhide : function(){
console.log(this.boxHidden);
if(this.boxHidden){
this.boxHidden=false;
this.buttonText="Hide";
}else{
this.boxHidden=true;
this.buttonText="Show";
}
},
hoverBox : function(){
this.boxHeight = boxHeight + 10;
}
}
});
Any tips as to why this doesn't work? Right now nothing happens when I hover over the square.

Try using v-on:mouseover instead of v-on:hover. Also your function appears to be named hoverBox not hoverGrow. So v-on:mouseover="hoverBox();" should work in your redBox div.

Inline style in vue

I try:
<a v-for='(item, index) in categories' :key='index'>
<div class='slider-categories__slide' :style='{ background: item.background}'>
</div>
</a>
Didn't work. Is it possible? If not, how i can add background for elements? (different background for items)

you can have an object named for example style in each object in the array, in each style object you can have specific style for that object and bind that to the style attribute on the element like :style="item.style".
also if you can't have a dedicated object for the styles in you array's objects you can use the data that you have to construct the appropriate object binding in the v-for, just pay attention to the correct formatting.
check the demo below: (here I used destructuring in v-for but its not necessary)
Vue.config.productionTip = false;
new Vue({
el: '#app',
data: {
items: [{
id: 1,
style: {
background: 'blue'
}
},
{
id: 2,
style: {
background: "url('https://picsum.photos/id/1025/200')",
backgroundSize: 'contain'
}
},
{
id: 3,
style: {
background: "linear-gradient(#e66465, #9198e5)"
},
},
]
},
})
.items {
height: 100px;
width: 100px;
display: inline-block;
border: 2px solid red;
}
<script src="https://cdn.jsdelivr.net/npm/vue#2.x/dist/vue.js"></script>
<div id="app">
<div class="items" v-for="{id, style} in items" :key="id" :style="style"></div>
</div>

How to prevent Computed property getting undefined in vue.js?

I'm calculating the container width and height using computed property and assigns it to the canvas in vue js.
export default {
...
computed: {
dimensions() {
return document.getElementById(
'canvas-container'
);
},
},
...
}
<div id="canvas-container">
<canvas
v-bind:id="id"
:height="dimensions.clientHeight"
:width="dimensions.clientWidth"
></canvas>
</div>
But the issue is that I'm getting an undefined error like:
cannot read the property clientHeight of null.
How can I avoid this.?

The canvas-container element doesn't exist yet when the dimensions computed property accesses it. The first render pass generates the virtual DOM but no actual DOM nodes are created yet.
You need to defer accessing the element until the component has mounted and the DOM element will exist.
There's no use using a computed property here since the DOM element is not reactive (it won't automatically update when the element resizes).
If possible, use a ref instead of using getElementById.
new Vue({
el: '#app',
data: {
width: 0,
height: 0,
},
mounted() {
// Element is now available
const el = this.$refs.el
this.width = el.clientWidth
this.height = el.clientHeight
}
})
#app {
border: 1px solid black;
width: 200px;
height: 100px;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>
<div id="app" ref="el">
Element size: {{ width }} x {{ height }}
</div>
If you need the dimensions to automatically update, you'll have to use some other mechanism for observing size changes such as a window resize listener or ResizeObserver.

Vue: #mouseover.stop still bubbling

I need to trigger a mouseover in Vue, but only on an element and its children, but not its parent. According to documentation this should work with the .stop modifier, but for some reason it still bubbles. .self wont work on child elements.
Any ideas what I might be doing wrong?
The code is simple:
<div v-for="(element) in elements" :key="element.id" :class="element.states"
#mouseover.stop="element.states.hover = true"
#mouseleave.stop="element.states.hover = false"></div>
Or on a component:
<my-component v-for="(element) in elements" :key="element.id" :class="element.states"
#mouseover.native.stop="element.states.hover = true"
#mouseleave.native.stop="element.states.hover = false"></my-component>

I've created a simple snippet to show how you can use #mouseover and #mouseleave with the stop event modifier and it seems to work, i.e. you only see BodyOver and BodyLeave in the console when entering and leaving the outer element.
new Vue({
el: "#app",
data: () => {
return {
parents: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
}
},
methods: {
over(ev) {
console.log(`Over ${ev.target.classList[0]}`);
},
leave(ev) {
console.log(`Leave ${ev.target.classList[0]}`);
},
bodyOver(ev) {
console.log(`Body Over ${ev.target.classList[0]}`);
},
bodyLeave(ev) {
console.log(`Body Leave ${ev.target.classList[0]}`);
}
}
});
.body {
padding: 20px;
background: red;
}
.parent {
padding: 20px;
background: green;
}
.child {
padding: 20px;
background: orange;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>
<div id="app">
<div class="body" #mouseover="bodyOver" #mouseleave="bodyLeave">
Body
<div class="parent" #mouseover.stop="over" #mouseleave.stop="leave" v-for="parent in parents">
Parent
<div class="child">
Child
</div>
</div>
</div>
</div>

After some extensive testing and try&error I found the reason why it was not working:
Due to the DOM nesting the mouseleave event is not fired, when hovering over a child. Also thanks #Shoejep for the test with logging, where you can see this behaviour.
To fix it, I had to use mouseout event on the children which gets fired on the parent when entering a child.

VueJS: Why parent components method unable to delete/destroy child's child (`vue2-dropzone`) component entirely?

I am creating a slider in vuejs and am using vue2-dropzone plugin for file uploads where each slide (slide-template.vue) has a vue2-dropzone component.
When app loads, image files are manually added in each vue2-dropzone (manuallyAddFile plugins API) queried from image API (hosted on heroku)
The issue is when I delete the first slide, calling the parent's (slider.vue) method removeSlideFn (passed down to child as prop) from child (slide-template.vue) component first slide is deleted but not entirely the dropzone images of the first slides are not destroyed and remains in the DOM, instead images of slide2, (the next slide) are deleted from the DOM (Pls try it once on codesandbox demo to actually know what I am mean). This does not happen when I delete slide2 or slide3 but only on slide1.
CodeSandBox Demo
App.vue
<template>
<div id="app">
<img width="15%" src="./assets/logo.png">
<slider />
</div>
</template>
<script>
import slider from "./components/slider";
export default {
name: "App",
components: {
slider
}
};
</script>
components\slider.vue (parent)
<template>
<div>
<hooper ref="carousel" :style="hooperStyle" :settings="hooperSettings">
<slide :key="idx" :index="idx" v-for="(slideItem, idx) in slideList">
<slide-template
:slideItem="slideItem"
:slideIDX="idx"
:removeSlideFn="removeCurrSlide" />
</slide>
<hooper-navigation slot="hooper-addons"></hooper-navigation>
<hooper-pagination slot="hooper-addons"></hooper-pagination>
</hooper>
<div class="buttons has-addons is-centered is-inline-block">
<button class="button is-info" #click="slidePrev">PREV</button>
<button class="button is-info" #click="slideNext">NEXT</button>
</div>
</div>
</template>
<script>
import {
Hooper,
Slide,
Pagination as HooperPagination,
Navigation as HooperNavigation
} from "hooper";
import "hooper/dist/hooper.css";
import slideTemplate from "./slide-template.vue";
import { slideShowsRef } from "./utils.js";
export default {
data() {
return {
sliderRef: "SlideShow 1",
slideList: [],
hooperSettings: {
autoPlay: false,
centerMode: true,
progress: true
},
hooperStyle: {
height: "265px"
}
};
},
methods: {
slidePrev() {
this.$refs.carousel.slidePrev();
},
slideNext() {
this.$refs.carousel.slideNext();
},
//Removes slider identified by IDX
removeCurrSlide(idx) {
this.slideList.splice(idx, 1);
},
// Fetch data from firebase
getSliderData() {
let that = this;
let mySliderRef = slideShowsRef.child(this.sliderRef);
mySliderRef.once("value", snap => {
if (snap.val()) {
this.slideList = [];
snap.forEach(childSnapshot => {
that.slideList.push(childSnapshot.val());
});
}
});
}
},
watch: {
getSlider: {
handler: "getSliderData",
immediate: true
}
},
components: {
slideTemplate,
Hooper,
Slide,
HooperPagination,
HooperNavigation
}
};
</script>
components/slide-template.vue (child, with vue2-dropzone)
<template>
<div class="slide-wrapper">
<slideTitle :heading="slideItem.heading" />
<a class="button delete remove-curr-slide" #click="deleteCurrSlide(slideIDX)" ></a>
<vue2Dropzone
#vdropzone-file-added="fileWasAdded"
#vdropzone-thumbnail="thumbnail"
#vdropzone-mounted="manuallyAddFiles(slideItem.zones)"
:destroyDropzone="false"
:include-styling="false"
:ref="`dropZone${ slideIDX }`"
:id="`customDropZone${ slideIDX }`"
:options="dropzoneOptions">
</vue2Dropzone>
</div>
</template>
<script>
import slideTitle from "./slide-title.vue";
import vue2Dropzone from "#dkjain/vue2-dropzone";
import { generate_ObjURLfromImageStream, asyncForEach } from "./utils.js";
export default {
props: ["slideIDX", "slideItem", "removeSlideFn"],
data() {
return {
dropzoneOptions: {
url: "https://vuejs-slider-node-lokijs-api.herokuapp.com/imageUpload",
thumbnailWidth: 150,
autoProcessQueue: false,
maxFiles: 1,
maxFilesize: 2,
addRemoveLinks: true,
previewTemplate: this.template()
}
};
},
components: {
slideTitle,
vue2Dropzone
},
methods: {
template: function() {
return `<div class="dz-preview dz-file-preview">
<div class="dz-image">
<img data-dz-thumbnail/>
</div>
<div class="dz-details">
<!-- <div class="dz-size"><span data-dz-size></span></div> -->
<!-- <div class="dz-filename"><span data-dz-name></span></div> -->
</div>
<div class="dz-progress"><span class="dz-upload" data-dz-uploadprogress></span></div>
<div class="dz-error-message"><span data-dz-errormessage></span></div>
<div class="dz-success-mark"><i class="fa fa-check"></i></div>
<div class="dz-error-mark"><i class="fa fa-close"></i></div>
</div>`;
},
thumbnail: function(file, dataUrl) {
var j, len, ref, thumbnailElement;
if (file.previewElement) {
file.previewElement.classList.remove("dz-file-preview");
ref = file.previewElement.querySelectorAll("[data-dz-thumbnail]");
for (j = 0, len = ref.length; j < len; j++) {
thumbnailElement = ref[j];
thumbnailElement.alt = file.name;
}
thumbnailElement.src = dataUrl;
return setTimeout(
(function(_this) {
return function() {
return file.previewElement.classList.add("dz-image-preview");
};
})(this),
1
);
}
},
// Drag & Drop Events
async manuallyAddFiles(zoneData) {
if (zoneData) {
let dropZone = `dropZone${this.slideIDX}`;
asyncForEach(zoneData, async fileInfo => {
var mockFile = {
size: fileInfo.size,
name: fileInfo.originalName || fileInfo.name,
type: fileInfo.type,
id: fileInfo.id,
childZoneId: fileInfo.childZoneId
};
let url = `https://vuejs-slider-node-lokijs-api.herokuapp.com/images/${
fileInfo.id
}`;
let objURL = await generate_ObjURLfromImageStream(url);
this.$refs[dropZone].manuallyAddFile(mockFile, objURL);
});
}
},
fileWasAdded(file) {
console.log("Successfully Loaded Files from Server");
},
deleteCurrSlide(idx) {
this.removeSlideFn(idx);
}
}
};
</script>
<style lang="scss">
.slide-wrapper {
position: relative;
}
[id^="customDropZone"] {
background-color: orange;
font-family: "Arial", sans-serif;
letter-spacing: 0.2px;
/* color: #777; */
transition: background-color 0.2s linear;
// height: 200px;
padding: 40px;
}
[id^="customDropZone"] .dz-preview {
width: 160px;
display: inline-block;
}
[id^="customDropZone"] .dz-preview .dz-image {
width: 80px;
height: 80px;
margin-left: 40px;
margin-bottom: 10px;
}
[id^="customDropZone"] .dz-preview .dz-image > div {
width: inherit;
height: inherit;
// border-radius: 50%;
background-size: contain;
}
[id^="customDropZone"] .dz-preview .dz-image > img {
width: 100%;
}
[id^="customDropZone"] .dz-preview .dz-details {
color: white;
transition: opacity 0.2s linear;
text-align: center;
}
[id^="customDropZone"] .dz-success-mark,
.dz-error-mark {
display: none;
}
.dz-size {
border: 2px solid blue;
}
#previews {
border: 2px solid red;
min-height: 50px;
z-index: 9999;
}
.button.delete.remove-curr-slide {
padding: 12px;
margin-top: 5px;
margin-left: 5px;
position: absolute;
right: 150px;
background-color: red;
}
</style>
slide-title.vue (not that important)
<template>
<h2 contenteditable #blur="save"> {{ heading }} </h2>
</template>
<script>
export default {
props: ["heading"],
methods: {
save() {
this.$emit("onTitleUpdate", event.target.innerText.trim());
}
}
};
</script>
utils.js (utility)
export async function generate_ObjURLfromImageStream(url) {
return await fetch(url)
.then(response => {
return response.body;
})
.then(rs => {
const reader = rs.getReader();
return new ReadableStream({
async start(controller) {
while (true) {
const { done, value } = await reader.read();
// When no more data needs to be consumed, break the reading
if (done) {
break;
}
// Enqueue the next data chunk into our target stream
controller.enqueue(value);
}
// Close the stream
controller.close();
reader.releaseLock();
}
});
})
// Create a new response out of the stream
.then(rs => new Response(rs))
// Create an object URL for the response
.then(response => {
return response.blob();
})
.then(blob => {
// generate a objectURL (blob:url/<uuid> list)
return URL.createObjectURL(blob);
})
.catch(console.error);
}
Technically this is how the app works, slider.vue loads & fetches data from database (firebase) and stores in a data array slideList, loops over the slideList & passes each slideData (prop slideItem) to vue-dropzone component (in slide-template.vue), when dropzone mounts it fires the manuallyAddFiles(slideItem.zones) on the #vdropzone-mounted custom event.
The async manuallyAddFiles() fetches image from an API (hosted on heroku), creates (generate_ObjURLfromImageStream(url)) a unique blob URL for the image (blob:/) and then calls plugins API dropZone.manuallyAddFile() to load the image into the corresponding dropzone.
To delete the current slide, child's deleteCurrSlide() calls parent's (slider.vue) removeSlideFn (passed as prop) method with the idx of current slide. The removeSlideFn use splice to remove the item at the corresponding array idx this.slideList.splice(idx, 1).
The problem is when I delete the first slide, first slide is deleted but not entirely, the dropzone images of the first slides are not destroyed and still remains in the DOM, instead the images of slide2, (the next slide) are deleted from the DOM.
CodeSandBox Demo
I am not sure what is causing the issue, may it's due to something in the vue's reactivity system OR Vue's Array reactivity caveat that is causing this.
Can anybody pls help me understand & resolve this and if possible point out the reason to the root of the problem.
Your help is much appreciated.
Thanks,

I think you probably missunderstand what is going on:
In VueJS there is a caching method which allow the reusing of existing component generated: - Each of your object are considered equals when rendered (at a DOM level).
So VueJS remove the last line because it is probably ask the least calculation and then recalcul the expected state. There are many side case to this (sometime, the local state is not recalculated). To avoir this: As recommended in the documentation, use :key to trace the id of your object. From the documentation:
When Vue is updating a list of elements rendered with v-for, by default it uses an “in-place patch” strategy. If the order of the data items has changed, instead of moving the DOM elements to match the order of the items, Vue will patch each element in-place and make sure it reflects what should be rendered at that particular index. This is similar to the behavior of track-by="$index" in Vue 1.x.
This default mode is efficient, but only suitable when your list render output does not rely on child component state or temporary DOM state (e.g. form input values).
To give Vue a hint so that it can track each node’s identity, and thus reuse and reorder existing elements, you need to provide a unique key attribute for each item. An ideal value for key would be the unique id of each item. This special attribute is a rough equivalent to track-by in 1.x, but it works like an attribute, so you need to use v-bind to bind it to dynamic values...
new Vue({
el: "#app",
data: {
counterrow: 1,
rows: [],
},
methods: {
addrow: function() {
this.counterrow += 1;
this.rows.push({
id: this.counterrow,
model: ""
});
},
removerows: function(index) {
this.rows.splice(index, 1);
},
},
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.16/vue.js"></script>
<div id="app">
<table>
<tr>
<td><input type="text" name="test1" /></td>
<td><button class="btn" #click="addrow">add row</button></td>
</tr>
<tr v-for="(row,index) in rows" :key="row.id">
<td><input type="text" name="test2" v-model="row.model" /></td>
<td><button class="btn" #click="removerows(index)">remove </button></td>
</tr>
</table>
</div>
In this code:
I corrected the fact counterrow was never incremented
I added a :key
The documentation of :key

What did you mean by
The problem is when I delete the first slide, first slide is deleted but not entirely, the dropzone images of the first slides are not destroyed and still remains in the DOM, instead the images of slide2, (the next slide) are deleted from the DOM.
From what I see, the elements are no longer in the DOM