Basic Javascript DOM manipulation concepts and commands


Specifications when Javascript runs in a web browser?

  • DOM spec: all page contents are represented as object and can be modified
  • BOM spec: additional objects provided by browser, non-DOM objects like the navigator or location objects
  • HTML spec: describes HTML language (tags) and BOM, various browser functions like setTimeout, alert, location

The DOM tree represent?

The document in the browser is the DOM tree. Tags become element nodes, text become text nodes. All nodes can be manipulated.

Wys of reaching a DOM node’s immediate neighbours

all nodes | element nodes only

parentNode | parentElement childNodes | children firstChild | firstElementChild lastChild | lastElementChild previousSibling | previousElementSibling nextSibling | nextElementSibling

Properties supported by the <table> element

element | properties | references

table | | .rows | <tr> | .caption | <caption> | .tHead | <thead> | .tFoot | <tfoot> | .tBodies | <tBody> thead | .rows | <tr> tfoot | .rows | <tr> tbody | .rows | <tr> tr | .cells | <td>, <th> | .sectionRowIndex | position index of <tr> | .rowIndex | number of <tr> in table, including all table rows td | .cellIndex | number of cell inside <tr> th | .cellIndex | number of cell inside <tr>

Main methods to search for nodes in DOM

Method | Searches By | Can call on element? | Live?

querySelector | CSS-selector | yes | no querySelectorAll | CSS-selector | yes | no getElementById | id | no | no getElementsByName | name | no | yes getElementsByTagName | tag or ‘*’ | yes | yes getElementsByClassName | class | yes | yes

Additionally: elem.matches(css) checks if elem matches a given CSS selector elem.closest(css) looks for nearest ancestor that matches CSS selector, including the elem itself elemA.contains(elemB), returns true if elemB is inside elemA, or if elemA === elemB

Differences between a live and a static collection

Methods like querySelectorAll returns a static collection, as opposed to getElementsByTagName.

<div>First div</div>
let divs = document.getElementsByTagName('div');
alert(divs.length); // 1
<div>Second div</div>
alert(divs.length); // 2
<div>First div</div>
let divs = document.querySelectorAll('div');
alert(divs.length); // 1
<div>Second div</div>
alert(divs.length); // 1

Main DOM node properties

DOM node properties | HTMLInputElement() | HTMLAnchorElement()

nodeType | value | href nodeName (all) | type | tagName (for elements) innerHTML outerHTML textContent nodeValue (mostly uses data below) data (content of non-element node, modifiable) hidden (when true, equals display: none)

Differences between attributes (HTML) and properties (DOM)

In general, attributes are what’s written in HTML, and properties are what’s in DOM objects.

 | Properties | Attributes ----------------------------------------------------------------------------------- Type | Any value, standard properties have types described in the spec | A string Name | Name is case-sensitive | Name is not case-sensitive

We mostly use properties, but can choose attributes only if DOM properties do not suit, or when exact attributes are needed.

  • Non-standard attribute, if starts with data-, use dataset
  • Read value as written in HTML, e.g. the href field is always a full URL and we want the full value

Methods that work with attributes:

elem |

 | .hasAttribute(name)
 | .getAttribute(name)
 | .setAttribute(name, value)
 | .removeAttribute(name)
 | .attributes

E.g. get the attribute of an element with a non-standard attribute

Choose genre