Chapter 5. JavaScript and Directly Accessing the User Interface

The user interface in JavaScript applications is typically the web page in which the script is embedded. The page may open in an Android tablet or a traditional computer browser, but the concepts are the same.

Nowadays, most people use libraries and frameworks in order to manipulate the web page. However, no matter how helpful and sophisticated the library, you still need to have a good idea of what you can, and cannot, do to the web page before making effective use of a library. More importantly, you need to have a good idea of the best practices to use when modifying the web page.

Accessing a Given Element and Finding Its Parent and Child Elements

Problem

You want to access a specific web page element, and then find its parent and child elements.

Solution

Give the element a unique identifier:

<div id="demodiv">
  <p>
    This is text.
  </p>
</div>

Use document.getElementById() to get a reference to the specific element:

var demodiv = document.getElementById("demodiv");

Find its parent via the parentNode property:

var parent = demodiv.parentNode;

Find its children via the childNodes property:

var children = demodiv.childNodes;

Discussion

A web document is organized like an upside-down tree, with the topmost element at the root and all other elements branching out beneath. Except for the root element (HTML), each element has a parent node, and all of the elements are accessible via the document.

There are several different techniques available ...

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