DOM Scripting

Nov 22, 2022

Michael Parker, own this book and took these notes to further my own learning. If you enjoy these notes, please purchase the book!

ECMAScript is the proper name of Javascript, which is not related to Java.
DHTML was a shorthand term for describing the combination of HTML, CSS, and Javascript.
DOM is generic: a model that can be used by any programming language to manipulate any document in any markup language.

Semicolons aren't required in Javascript unless multiple statements appear on one line, but are good practice.
Use C or C++ commenting styles, which are //comment and /*comment*/, respectively.
Declare numeric or associative arrays by using the same Array class.
Prepending a variable declaration with var will treat the variable as a local variable.
Objects have properties (variables) and methods (actions as functions).
Native objects are those part of the Javascript library, such as Array, Date, and Math.
Host objects are those supplied by the web browser, such as Form, Image, and Element.

The properties and methods of the window object are often referred to as the Browser Object Model.
Element attributes are represented by attribute nodes, or children of the element, in the DOM.
Method getElementsByTagName accepts the wildcard value *.
Method getAttribute will return null if an attribute does not exist.

In an onclick handler, you can use the this keyword to refer to the element node.
Returning false from the onclick handler of an img element will disable the default behavior of following the src URL.
The body element of the document can be retrieved using document.body.
Whitespace and line breaks between elements in the HTML source are interpreted in nodes in the childNodes array.
The nodeType attribute has 12 values, where 1 is an element node, 2 is an attribute node, and 3 is a text node.
The nodeValue attribute contains the text value of a text node.

Making your web site navigable by users without Javascript is called graceful degradation.
The JavaScript pseudo-protocol allows invoking JavaScript from within a link, but does not allow graceful degradation.
Likewise, defining a link as # and using an inline event handler does not allow graceful degradation.
Progressive enhancement is using JavaScript and the DOM to enhance sites that are already functional without them.
When window.onload is invoked, the document (and hence DOM) within it is guaranteed to exist.
Testing whether the browser supports some DOM property or method in a conditional is called object detection.

When applying an anonymous function, the this keyword will refer to the element it is bound to.
To invoke multiple functions on loading, you must bind a single function to window.onload that invokes each.
To be cautious, test not only whether DOM methods exist, but expected DOM nodes and their attributes exist.
Don't use the onkeypress event handler -- it can be invoked even if the user presses the Tab key.
The onclick event handler is also invoked if you press Return while tabbing from link to link.
HTML-DOM extends the DOM Core with properties like document.forms and document.images.

You must invoke the document.write method from a script element in the body, which is obtrusive, so avoid it.
The innerHTML element isn't a web standard, and referencing the inserted elements still requires the DOM, so avoid it.
Both document.write and innerHTML won't work with XHTML served with MIME type application/xhtml+xml.
The createElement method creates an element not attached to the DOM tree, called a DocumentFragment.
Text elements are created with method createTextMode, not createElement.
There is an insertBefore method for inserting elements, but you have write your own insertAfter method.

An abbreviation is any shortened version of a word, while an acronym is an abbreviation pronounced as a word.
You can iterate through the keys of an Array object using the construct for (variable in array).
Sniffing for a specific browser name and version number is bound to cause problems and convoluted code.
Using DOM you can add meaningful content from attributes that browsers typically ignore, like cite for blockquote.
Convention for the accesskey attribute is 1 for home, 4 for search, and 9 for contact.
The accessibility statement lists which access keys have been assigned on a page.

Every element has a style property -- it is an object, and not a simple string.
CSS properties are converted to camel case, so the font-family property becomes element.style.fontFamily.
Usually style properties are returned in the same units in which they are set, for example em vs px.
The DOM can only return inline style information, not style applied through external CSS files or style tags.
But the DOM can retrieve styles that the DOM itself assigns through the style property.
CSS pseudo-classes and DOM scripting can overlap when styling elements based on state, like :hover versus :onmouseover.
The DOM can apply styles defined in CSS files by setting the element's class attribute, or its className style property.

Elements have a position of static by default, but by using relative we can use the float property on them.
The setTimeout method returns a handle to the function that can be cancelled using clearTimeout.
Methods parseInt and parseFloat extract the number starting any string, e.g. 39 steps converts to 39.
The overflow property specifies how to handle content that is larger than the containing element.
To persist variables between method calls, set them as element properties instead of making them global.

You can split your CSS into multiple files: one for layout, one for color, and one for typography.
The address of the current window can be retrieved through property window.location.href.
To frame a slideshow element, make the frame image an absolutely positioned child with a high z-index.
Invoking the focus method on a form text element will place the cursor inside it.
The form.elements array contains only descendant form elements, which differs from form.childNodes.

If the boolean argument to cloneNode is true, all children nodes are copied; if false, only its attributes are.
The newly created node returned by cloneNode is not automatically added to the document.
Methods appendChild, insertBefore, and replaceChild will move elements that already exist in the DOM.
If the hasChildNodes property is false, childNodes is an empty array, and firstChild and lastChild are null.
The nodeName property for a element node is its tag type, and for an attribute node is the attribute name.
The nodeValue property for an attribute node is its value, and for a text node is its text, but is null for element nodes.
You can't set nodeValue if it is already null, i.e. you can't assign a value to element nodes.
The nodes adjacent to an element node can be retrieved with nextSibling and previousSibling.

Codestar’s Newsletter