in DevTool, $0 returns the selected Element, so you can use normal DOM APIs to access: ex, $0.classList
DOM Ready
event DOMContentLoaded : the browser fully loaded HTML, and the DOM tree is built, but external resources like pictures <img> and stylesheets may be not yet loaded.
function load: the browser loaded all resources (images, styles etc)
window.onload = function() {}
function beforeunload/unload : when the user is leaving the page
window.unload = function() {}
// handle the case when we add the callback after the document is already loaded
if (document.readyState === "complete" ||
(document.readyState !== "loading" && !document.documentElement.doScroll)
) {
callback();
} else {
document.addEventListener("DOMContentLoaded", callback);
}
// CRUD class
myElement.classList.add('foo', 'bar')
myElement.classList.remove('bar')
myElement.classList.toggle('baz')
myElement.classList.replace('bar', 'baz')
// fetch class
myElement.className // -> 'foo bar'
myElement.classList.contains('foo') // -> 'foo bar'
// show or hide button
stopBtn.style.display = 'none'; // '';
// set style (this won't get all styles)
myElement.style.marginLeft = '2em'
// get all styles as text
var text = myElement.style.cssText; // "color: red;"
// get all styles
window.getComputedStyle(myElement).getPropertyValue('margin-left')
// Animation
const start = window.performance.now()
const duration = 2000
window.requestAnimationFrame(function fadeIn (now)) {
const progress = now - start
myElement.style.opacity = progress / duration
if (progress < duration) {
window.requestAnimationFrame(fadeIn)
}
}
Element CRUD
// create
const myNewElement = document.createElement('a');
myNewElement.setAttribute('href', 'http://zurassic.com/');
// append as child
element1.appendChild(element2)
// this can also move existing element
element1.appendChild(document.querySelecotr('.existing'));
// insert into precise location, can be same level or as children
// [insertAdjacentHTML](https://developer.mozilla.org/en-US/docs/Web/API/Element/insertAdjacentHTML)
document.querySelector("body").insertAdjacentHTML("beforeend", '<div class="loader"></div>');
// this can also move existing element
document.querySelector("body").insertAdjacentHTML("beforeend", document.querySelecotr('.existing'));
// remove
myElement.parentNode.removeChild(myElement)
// clone
const myElementClone = myElement.cloneNode()
// preferment version using [DocumentFragment](https://developer.mozilla.org/en-US/docs/Web/API/DocumentFragment)
// It's minimal DOM, similar to StringBuilder
const fragment = document.createDocumentFragment()
fragment.appendChild(text)
fragment.appendChild(hr)
myElement.appendChild(fragment)
The MutationObserver interface provides the ability to watch for changes being made to the DOM tree.
You can observe changes (child, attributes, style, etc) and pause in dev tools:
function observe(el) {
var MutationObserver = window.WebKitMutationObserver;
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(mutation) {
console.log(
"old",
mutation.oldValue,
"new",
mutation.target.style.cssText,
"mutation",
mutation
);
if (mutation.attributeName == property) debugger;
});
});
var config = {
attributes: true,
attributeFilter: ["class"], // only observe class changes
attributeOldValue: true
};
observer.observe(el, config);
}
observe(document.querySelector(".my-test"));
Common Functions
// Rename a tag (change tag type). Ex, <div> -> <a>
function renameTag(target, newNode) {
// copy attributes
for (var i = 0; i < target.attributes.length; i++) {
newNode.setAttribute(
target.attributes[i].nodeName,
target.attributes[i].nodeValue
);
}
// move children. firstChild is a live API so we can 'while' on that
while (target.firstChild) {
newNode.appendChild(target.firstChild);
}
// copy in-line styles
if (target.style.length > 0) {
newNode.style.cssText = target.style.cssText;
}
return target.parentNode.replaceChild(newNode, target);
}
Don't use onclick: single property, essentially override it.
Event CRUD
// add
myElement.addEventListener('click', (event)=> {
console.log(event.type + ' got fired')
})
// remove
myElement.addEventListener('change', function listener (event) {
console.log(event.type + ' got triggered on ' + this)
this.removeEventListener('change', listener)
})
// match all children (live too)
myForm.addEventListener('change', function (event) {
const target = event.target
if (target.matches('input')) {
console.log(target.value)
}
})
Override Default Event
preventDefault() stop default handling, it'll still propagate
stopPropagation() stop bubbling up
stopImmediatePropagation() stop handling in current layer, stop passing to other event handlers: If several listeners are attached to the same element for the same event type, they are called in order in which they have been added. If during one such call, event.stopImmediatePropagation() is called, no remaining listeners will be called.
e.target vs e.currentTarget:
e.target identifies the element on which the event occurred
e.currentTarget always refer to the the element to which the event handler has been attached
this
usually points to the DOM element where the handler is bound.
NOTE if you add event using arrow function then it's document instead of the element!
Event delegation can also be used to add behavior to any element (with data-attr):
// use with <button data-counter>add</button>
document.addEventListener('click', function(event) {
if (event.target.dataset.counter != undefined) {
// if the attribute exists...
event.target.value++;
}
});
