Do getElementsByClassName (and similar functions like getElementsByTagName and querySelectorAll) work the same as getElementById or do they return an array of elements?
The reason I ask is because I am trying to change the style of all elements using getElementsByClassName. See below.
//doesn't work
document.getElementsByClassName('myElement').style.size = '100px';
//works
document.getElementById('myIdElement').style.size = '100px';
Your getElementById code works since IDs have to be unique and thus the function always returns exactly one element (or null if none was found).
However, the methods
getElementsByClassName,
getElementsByName,
getElementsByTagName, and
getElementsByTagNameNS
return an iterable collection of elements.
The method names provide the hint: getElement implies singular, whereas getElements implies plural.
The method querySelector also returns a single element, and querySelectorAll returns an iterable collection.
The iterable collection can either be a NodeList or an HTMLCollection.
getElementsByName and querySelectorAll are both specified to return a NodeList; the other getElementsBy* methods are specified to return an HTMLCollection, but please note that some browser versions implement this differently.
Both of these collection types don’t offer the same properties that Elements, Nodes, or similar types offer; that’s why reading style off of document.getElements…(…) fails.
In other words: a NodeList or an HTMLCollection doesn’t have a style; only an Element has a style.
These “array-like” collections are lists that contain zero or more elements, which you need to iterate over, in order to access them.
While you can iterate over them similarly to an array, note that they are different from Arrays.
In modern browsers, you can convert these iterables to a proper Array with Array.from; then you can use forEach and other Array methods, e.g. iteration methods:
Array.from(document.getElementsByClassName("myElement"))
.forEach((element) => element.style.size = "100px");
In old browsers that don’t support Array.from or the iteration methods, you can still use Array.prototype.slice.call.
Then you can iterate over it like you would with a real array:
var elements = Array.prototype.slice
.call(document.getElementsByClassName("myElement"));
for(var i = 0; i < elements.length; ++i){
elements[i].style.size = "100px";
}
You can also iterate over the NodeList or HTMLCollection itself, but be aware that in most circumstances, these collections are live (MDN docs, DOM spec), i.e. they are updated as the DOM changes.
So if you insert or remove elements as you loop, make sure to not accidentally skip over some elements or create an infinite loop.
MDN documentation should always note if a method returns a live collection or a static one.
For example, a NodeList offers some iteration methods such as forEach in modern browsers:
document.querySelectorAll(".myElement")
.forEach((element) => element.style.size = "100px");
A simple for loop can also be used:
var elements = document.getElementsByClassName("myElement");
for(var i = 0; i < elements.length; ++i){
elements[i].style.size = "100px";
}
Aside: .childNodes yields a live NodeList and .children yields a live HTMLCollection, so these two getters also need to be handled carefully.
There are some libraries like jQuery which make DOM querying a bit shorter and create a layer of abstraction over “one element” and “a collection of elements”:
$(".myElement").css("size", "100px");
You are using a array as an object, the difference between getElementbyId and
getElementsByClassName is that:
getElementbyId will return an Element object or null if no element with the ID is found
getElementsByClassName will return a live HTMLCollection, possibly of length 0 if no matching elements are found
getElementsByClassName
The getElementsByClassName(classNames) method takes a string that
contains an unordered set of unique space-separated tokens
representing classes. When called, the method must return a live
NodeList object containing all the elements in the document that
have all the classes specified in that argument, having obtained the
classes by splitting a string on spaces. If there are no tokens
specified in the argument, then the method must return an empty
NodeList.
https://www.w3.org/TR/2008/WD-html5-20080610/dom.html#getelementsbyclassname
getElementById
The getElementById() method accesses the first element with the specified id.
https://developer.mozilla.org/en-US/docs/Web/API/Document/getElementById
in your code the lines:
1- document.getElementsByClassName('myElement').style.size = '100px';
will NOT work as expected, because the getElementByClassName will return an array, and the array will NOT have the style property, you can access each element by iterating through them.
That's why the function getElementById worked for you, this function will return the direct object. Therefore you will be able to access the style property.
ES6 provides Array.from() method, which creates a new Array instance from an array-like or iterable object.
let boxes = document.getElementsByClassName('box');
setTimeout(() => {
Array.from(boxes).forEach(v => v.style.background = 'green');
console.log(Array.from(boxes));
}, 500);
.box {
width: 50px;
height: 50px;
margin: 5px;
background: blue;
display: inline-block;
}
<div class='box'></div>
<div class='box'></div>
<div class='box'></div>
<div class='box'></div>
As you can see inside the code snippet, after using Array.from() function you are then able to manipulate over each element.
The same solution using **`jQuery`**.
$('.box').css({'background':'green'});
.box {
width: 50px;
height: 50px;
margin: 5px;
background: blue;
display: inline-block;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class='box'></div>
<div class='box'></div>
<div class='box'></div>
<div class='box'></div>
The following description is taken from this page:
The getElementsByClassName() method returns a collection of all elements in the document with the specified class name, as a NodeList object.
The NodeList object represents a collection of nodes. The nodes can be
accessed by index numbers. The index starts at 0.
Tip: You can use the length property of the NodeList object to determine the number of elements with a specified class name, then you can loop through all elements and extract the info you want.
So, as a parameter getElementsByClassName would accept a class name.
If this is your HTML body:
<div id="first" class="menuItem"></div>
<div id="second" class="menuItem"></div>
<div id="third" class="menuItem"></div>
<div id="footer"></div>
then var menuItems = document.getElementsByClassName('menuItem') would return a collection (not an array) of the 3 upper <div>s, as they match the given class name.
You can then iterate over this nodes (<div>s in this case) collection with:
for (var menuItemIndex = 0 ; menuItemIndex < menuItems.length ; menuItemIndex ++) {
var currentMenuItem = menuItems[menuItemIndex];
// do stuff with currentMenuItem as a node.
}
Please refer to this post for more on differences between elements and nodes.
In Other Words
document.querySelector() selects only the first one element of the specified selector. So it doesn't spit out an array, it's a single value. Similar to document.getElementById() which fetches ID-elements only, since IDs have to be unique.
document.querySelectorAll() selects all elements with the specified selector and returns them in an array. Similar to document.getElementsByClassName() for classes and document.getElementsByTagName() tags only.
Why use querySelector?
It's used merely for the sole purpose of ease and brevity.
Why use getElement/sBy?*
Faster performance.
Why this performance difference?
Both ways of selection has the purpose of creating a NodeList for further use.
querySelectors generates a static NodeList with the selectors thus it must be first created from scratch.
getElement/sBy* immediately adapts the existing live NodeList of the current DOM.
So, when to use which method it's up to you/your project/your device.
Infos
Demo of all methods
NodeList Documentation
Performance Test
You could get a single element by running
document.querySelector('.myElement').style.size = '100px';
but it's going to work for the first element with class .myElement.
If you would like apply this for all elements with the class I suggest you to use
document.querySelectorAll('.myElement').forEach(function(element) {
element.style.size = '100px';
});
It returns Array-like list.
You make that an Array as example
var el = getElementsByClassName("elem");
el = Array.prototype.slice.call(el); //this line
el[0].appendChild(otherElem);
/*
* To hide all elements with the same class,
* use looping to reach each element with that class.
* In this case, looping is done recursively
*/
const hideAll = (className, i=0) => {
if(!document.getElementsByClassName(className)[i]){ //exits the loop when element of that id does not exist
return;
}
document.getElementsByClassName(className)[i].style.visibility = 'hidden'; //hide element
return hideAll(className, i+1) //loop for the next element
}
hideAll('appBanner') //the function call requires the class name
With any browser supporting ES5+ (any browser basically above IE8) you can use the Array.prototype.forEach method.
Array.prototype.forEach.call(document.getElementsByClassName('answer'), function(el) {
el.style.color= 'red';
});
caniuse source
So I was told that this is a duplicate from my question and I should delete mine, which I will do so I can keep the forum clean and keep the right to make questions.
As I think mine and this question are really different I will point out the answer to mine, so I will complete the knowledge in this page and the information will not be lost.
Question
I have a code in the snippet that has a document.getElementsByClassName("close")[0], what the [0] is doing?
I never seen a square brackets being used in getElementsByClassName for what purpose is it used for?
Also, how can I convert it to jQuery?
Answer
The code in the snippet has a [0] it is actually being used as a array and as it is a 0 it is referring to the first time the appointed class is being used.
Same thing above.
I couldn't really do it and no one answered it. In the part of the code that is refering to event. target I can not use $("#myModal") instead of document.getElementById("myModal"), I think they should equivalent, but in this case the jQuery form substituting the standard one will not result in the desired effect.
window.onclick = function(event) {
if (event.target == modal) {
modal.style.display = "none";
}
}
var modal = document.getElementById("myModal");
var btn = document.getElementById("myBtn");
var span = document.getElementsByClassName("close")[0];
btn.onclick = function() {
modal.style.display = "block";
}
span.onclick = function() {
modal.style.display = "none";
}
window.onclick = function(event) {
if (event.target == modal) {
modal.style.display = "none";
}
}
body {font-family: Arial, Helvetica, sans-serif;}
.modal {
display: none;
position: fixed;
z-index: 1;
padding-top: 100px;
left: 0;
top: 0;
width: 100%;
height: 100%;
overflow: auto;
background-color: rgb(0,0,0);
background-color: rgba(0,0,0,0.4);
}
.modal-content {
background-color: #fefefe;
margin: auto;
padding: 20px;
border: 1px solid #888;
width: 80%;
}
.close {
color: #aaaaaa;
float: right;
font-size: 28px;
font-weight: bold;
}
.close:hover,
.close:focus {
color: #000;
text-decoration: none;
cursor: pointer;
}
<h2>Modal </h2>
<button id="myBtn">Open Modal</button>
<div id="myModal" class="modal">
<div class="modal-content">
<span class="close">×</span>
<p>Some text in the Modal..</p>
</div>
</div>
update
It seems I can't really delete mine question and people are unsatisfied with it, I really don't know what I should do.
Super old school solution:
[].forEach.call(document.getElementsByClassName('myClass'), function (el) {
el.style.size = '100px';
});
An answer for Drenzii's specific case...
You could make a function that will work for any of the word elements and pass in the number of the one you want to transform, like:
// Binds `wordButtons` to an (array-like) HTMLCollection of buttons
const wordButtons = document.getElementsByClassName("word");
// Applies the `slantWord` function to the first word button
slantWord(1);
// Defines the `slantWord` function
function slantWord(wordNumber) {
const index = wordNumber - 1; // Collection index is zero-based
wordButtons[index].style.transform = "rotate(7deg)"; // Transforms the specified button
}
<div class="wordGameContainer">
<button class="word word1">WORD 1</button>
<button class="word word2">WORD 2</button>
<button class="word word3">WORD 3</button>
<button class="word word4">WORD 4</button>
</div>
<div>
<button onclick="moveWord()" class="playButton">PLAY</button>
</div>
I have issue with rendering inside component. I would like to emit data from another component and send to another component, data was emitted, but the problem is when I create the element with Renderer2, sometimes it's working, but sometimes not. Probably it's a problem with rendering style element in a component?
toolbar.state.service.ts
My service method for emitting data
private globalStyles = new BehaviorSubject<string>('');
formDesign(data: any) {
this.globalStyles.next(data);
}
aside.component.ts
Here I emit data from Reactive Form control and send to another component.
// Height
this.formGlobal.controls['height'].valueChanges
.pipe(debounceTime(500))
.pipe(distinctUntilChanged())
.pipe(takeUntil(this.destroy$))
.subscribe(height => {
this.formGlobal.controls['height'].setValue(height);
this.formGlobal.updateValueAndValidity();
this.showDataCriteria = {
width: this.formGlobal.controls['width'].value + 'px',
height: height + 'px'
};
this.toolbarStatus.formDesign(this.showDataCriteria);
});
builder.component.ts
Here I'm getting data from aside.component.ts and it received!
/**
* Generate CSS
*/
generateCss() {
let basicStyles = ' ';
let newStyle: HTMLElement;
let style: HTMLElement = this.document.getElementById('custom-class');
style
? (newStyle = style)
: (newStyle = this.renderer.createElement('style'));
this.renderer.setAttribute(newStyle, 'id', 'custom-class');
let completeStyleFields = '';
this.customStyle.global
? (basicStyles += `#${this.projectInfo.id} {${this.customStyle.global}}`)
: (basicStyles += '');
console.log(basicStyles);
this.customStyle.sections.forEach(element => {
completeStyleFields += `#${element.id} {${element.textProps}}`;
});
basicStyles += completeStyleFields;
const text = (this.document.textContent = basicStyles);
newStyle.innerText = text;
this.renderer.appendChild(this.dndComponent.nativeElement, newStyle);
}
The Main problem is after style element was created, and I'm seeing the element in the DOM, styles not accepting! Sometimes accepting, and sometimes not. What should I do? How manipulate reload page probably to inject component and styles element?
Short UPD:
After all, I'm seeing #4152ae54-8a9d-49d5-a33d-62dfbbd35890 {height:600px; width:812px; }
But styles not accepted to the elements!
CSS can't render if the first numeric letter (#4152ae54-8a9d-49d5-a33d-62dfbbd35890). That’s because even though HTML5 is quite happy for an ID to start with a number, CSS is not. CSS simply doesn’t allow selectors to begin with a number. The relevant part of the specification states.
I like the simplicity of hyperHtml and lit-html that use 'Tagged Template Literals' to only update the 'variable parts' of the template. Simple javascript and no need for virtual DOM code and the recommended immutable state.
I would like to try using custom elements with hyperHtml as simple as possible
with support of the <slot/> principle in the templates, but without Shadow DOM. If I understand it right, slots are only possible with Shadow DOM?
Is there a way or workaround to have the <slot/> principle in hyperHTML without using Shadow DOM?
<my-popup>
<h1>Title</h1>
<my-button>Close<my-button>
</my-popup>
Although there are benefits, some reasons I prefer not to use Shadow DOM:
I want to see if I can convert my existing SPA: all required CSS styling lives now in SASS files and is compiled to 1 CSS file. Using global CSS inside Shadow DOM components is not easily possible and I prefer not to unravel the SASS (now)
Shadow DOM has some performance cost
I don't want the large Shadow DOM polyfill to have slots (webcomponents-lite.js: 84KB - unminified)
Let me start describing what are slots and what problem these solve.
Just Parked Data
Having slots in your layout is the HTML attempt to let you park some data within the layout, and address it later on through JavaScript.
You don't even need Shadow DOM to use slots, you just need a template with named slots that will put values in place.
<user-data>
<img src="..." slot="avatar">
<span slot="nick-name">...</span>
<span slot="full-name">...</span>
</user-data>
Can you spot the difference between that component and the following JavaScript ?
const userData = {
avatar: '...',
nickName: '...',
fullName: '...'
};
In other words, with a function like the following one we can already convert slots into useful data addressed by properties.
function slotsAsData(parent) {
const data = {};
parent.querySelectorAll('[slot]').forEach(el => {
// convert 'nick-name' into 'nickName' for easy JS access
// set the *DOM node* as data property value
data[el.getAttribute('slot').replace(
/-(\w)/g,
($0, $1) => $1.toUpperCase())
] = el; // <- this is a DOM node, not a string ;-)
});
return data;
}
Slots as hyperHTML interpolations
Now that we have a way to address slots, all we need is a way to place these inside our layout.
Theoretically, we don't need Custom Elements to make it possible.
document.querySelectorAll('user-data').forEach(el => {
// retrieve slots as data
const data = slotsAsData(el);
// place data within a more complex template
hyperHTML.bind(el)`
<div class="user">
<div class="avatar">
${data.avatar}
</div>
${data.nickName}
${data.fullName}
</div>`;
});
However, if we'd like to use Shadow DOM to keep styles and node safe from undesired page / 3rd parts pollution, we can do it as shown in this Code Pen example based on Custom Elements.
As you can see, the only needed API is the attachShadow one and there is a super lightweight polyfill for just that that weights 1.6K min-zipped.
Last, but not least, you could use slots inside hyperHTML template literals and let the browser do the transformation, but that would need heavier polyfills and I would not recommend it in production, specially when there are better and lighter alternatives as shown in here.
I hope this answer helped you.
I have a similar approach, i created a base element (from HyperElement) that check the children elements inside a custom element in the constructor, if the element doesn't have a slot attribute im just sending them to default slot
import hyperHTML from 'hyperhtml/esm';
class HbsBase extends HyperElement {
constructor(self) {
self = super(self);
self._checkSlots();
}
_checkSlots() {
const slots = this.children;
this.slots = {
default: []
};
if (slots.length > 0) {
[...slots].map((slot) => {
const to = slot.getAttribute ? slot.getAttribute('slot') : null;
if (!to) {
this.slots.default.push(slot);
} else {
this.slots[to] = slot;
}
})
}
}
}
custom element, im using a custom rollup plugin to load the templates
import template from './customElement.hyper.html';
class CustomElement extends HbsBase {
render() {
template(this.html, this, hyperHTML);
}
}
Then on the template customElement.hyper.html
<div>
${model.slots.body}
</div>
Using the element
<custom-element>
<div slot="body">
<div class="row">
<div class="col-sm-6">
<label for="" class="">Name</label>
<p>
${model.firstName} ${model.middleInitial} ${model.lastName}
</p>
</div>
</div>
...
</div>
</custom-element>
Slots without shadow dom are supported by multiple utilities and frameworks.
Stencil enables using without shadow DOM enabled. slotted-element gives support without framework.
I have a div
<div class="blue>;
The class blue is:
.blue {
background-color: blue;
}
Now I know I can set the background color of the div in the console using:
$0.style.backgroundColor = "#ffcc00"
But what if I want to get the value of the background color for that element using the console?
It's possible you may want computed style:
var style = getComputedStyle(document.body, null); // Gets the style for a passed element and optional pseudo selecter (eg. :hover)
console.log(style.backgroundColor);
It's important to note that computed style is the rendered result. If you have multiple rules for the same element, this will only display the ones that have been applied.
You can do :
var blue = document.getElementsByClassName('blue')[0];
blue.style.getPropertyCSSValue('background-color');
or you do:
blue.style.getPropertyValue('background-color');
I was creating a <div> tag in which I wanted to apply two classes for a <div> tag which would be a thumbnail gallery. One class for its position and the other class for its style. This way I could apply the style, I was having some strange results which brought me to a question.
Can two classes be assigned to a <div> tag? If so, which one overrules the other one or which one has priority?
Multiple classes can be assigned to a div. Just separate them in the class name with spaces like this:
<div class="rule1 rule2 rule3">Content</div>
This div will then match any style rules for three different class selectors: .rule1, .rule2 and .rule3.
CSS rules are applied to objects in the page that match their selectors in the order they are encountered in the style sheet and if there is a conflict between two rules (more than one rule trying to set the same attribute), then CSS specificity determines which rule takes precedence.
If the CSS specificity is the same for the conflicting rules, then the later one (the one defined later in the stylesheet or in the later stylesheet) takes precedence. The order of the class names on the object itself does not matter. It is the order of the style rules in the style sheet that matters if the CSS specificity is the same.
So, if you had styles like this:
.rule1 {
background-color: green;
}
.rule2 {
background-color: red;
}
Then, since both rules match the div and have exactly the same CSS specificity, then the second rule comes later so it would have precedence and the background would be red.
If one rule had a higher CSS specificity (div.rule1 scores higher than .rule2):
div.rule1 {
background-color: green;
}
.rule2 {
background-color: red;
}
Then, it would take precedence and the background color here would be green.
If the two rules don't conflict:
.rule1 {
background-color: green;
}
.rule2 {
margin-top: 50px;
}
Then, both rules will be applied.
Actually, the class that defined last in the css - is applied on your div.
check it out:
red last in css
.blue{ color: blue; }
.red { color: red; }
<div class="blue red">blue red</div>
<div class="red blue">red blue</div>
vs
blue last in css
.red { color: red; }
.blue{ color: blue; }
<div class="blue red">blue red</div>
<div class="red blue">red blue</div>
If you asking about they have same property then as per the CSS rule it's take the last statement.
<div class="red green"></div>
CSS
.red{
color:red;
}
.green{
color:green;
}
As per the above example it's take the last statement as per css tree which is .green.
The class that is defined last in the CSS have priority, if nothing else applies.
Read up on CSS priority to see how it works.
Many classes can be assigned to an element, you just separate them with a space
<div class="myClass aSecondClass keepOnClassing stayClassySanDiego"></div>
Because of the cascade in CSS, the overwriting rules closest the to bottom of the document will be applied to the element.
So if you have
.myClass
{
background: white;
color: blue;
}
.keepOnClassing
{
color: red;
}
The red color will be used, but not the background color as it was not overwritten.
You must also take into account CSS specificity, if you have a more specific selector, this one will be used:
.myClass
{
background: white;
color: blue;
}
div.myClass.keepOnClassing
{
background: purple;
color: red;
}
.stayClassySanDiego
{
background: black;
}
The second selector here will be used as it is more specific.
You can take a look at it all here.