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Document Object Model

  • document - refers to entire document, has head and body properties
  • document.documentElement - refers to object representing <html> tag; root of the DOM tree
  • foo.childNodes - refers to NodeList of child nodes of node foo
  • foo.firstChild - refers to first child of node foo (or null)
  • foo.lastChild - refers to last child of node foo (or null)
  • foo.previousSibling, foo.nextSibling - refer to adjacent nodes (or null)
  • foo.children - refers to only element children
  • foo.getElementsByTagName("bar") - refers to an array-like object of elements with the tag name bar in the subtree rooted at foo
  • foo.getElementById("bar") - refers to the object with id bar in the subtree rooted at foo
  • foo.getElementsByClassName("bar") - refers to an array-like object of elements with the class name bar in the subtree rooted at foo
  • foo.appendChild(bar) - append bar to end of foo's childNodes
  • foo.insertBefore(newBar, oldBar) - insert newBar before oldBar in subtree rooted at foo
  • foo.replaceChild(newBar, oldBar) - replace oldBar by newBar in subtree rooted at foo
  • document.createTextNode("foo") - returns a text node with text foo that can be inserted into the document
  • document.createElement("foo") - returns an element with tag foo
  • foo.getAttribute("bar") - returns value of attribute bar for element foo
  • foo.setAttribute("name", "value") - set name attribute of foo element to bar
  • foo.offsetWidth/foo.offsetHeight - returns width/height of element foo
  • foo.clientWidth/foo.clientHeight - returns width/height of element foo ignoring borders
  • foo.getBoundingClientRect - returns {top, bottom, left, right} indicating pixel properties of foo
  • foo.pageXOffset/foo.pageYOffset - returns scroll position
  • foo.style - refers to object that has properties for all possible style properties (hyphenated names are replaced with camelCase names)
  • foo.querySelectorAll("bar") - returns a NodeList containing all elements that match bar (non live version). Use querySelector (without the All) to get the first element that matches or null (if none match)
  • window - object for registering handlers on entire window
  • foo.addEventListener("baz", bar) - call function bar for event baz on element foo
  • foo.removeEventListener("baz", bar) - remove function bar for event baz on element foo
  • Event object - holds additional information about the event, for example
let button = document.querySelector("button");
button.addEventListener("mousedown", event => {
    if (event.button == 0) {
        console.log("Left button");
    } else if (event.button == 1) {
        console.log("Middle button");
    } else if (event.button == 2) {
        console.log("Right button");
    });
  • event.type - stores string identifying event
  • foo.stopPropogation() - stop event propogation to parent elements
  • foo.target - refers to node where event originated
  • keyup, keydown - events received on key presses
  • event.ctrlKey/event.shiftKey/event.altKey etc - check whether key is being held down
  • mousedown/mouseup - events that occur on mouse clicks on DOM nodes immediately below the mouse pointer when the event occurs
  • click - event fires on the most specific node that contained both the press and the release of the button
  • dblclick - event fires when two clicks happen close together
  • clientX/clientY - refers to coordinates of the place where a mouse event happened relative to top-left corner of the window
  • mousemove - event fired each time mouse moves
  • foo.preventDefault() - prevent default action for event foo
  • foo.buttons - refers to mouse buttons being held down