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Chapter 1
HTML Trees and DOM Selection
Overview
The DOM is the browser’s tree-shaped map of a web page. HTML makes the map, CSS decorates it, and JavaScript finds parts of it to change. We use DOM selection when we need to update a heading, button, picture, or other page part.
Quick Reference
| Tool | What it finds | Example | |---|---|---| | getElementById() | One item with an id | document.getElementById("title") | | querySelector() | The first matching item | document.querySelector(".card") | | querySelectorAll() | All matching items | document.querySelectorAll("li") | | getElementsByClassName() | Items with a class | document.getElementsByClassName("item") | | getElementsByTagName() | Items with a tag | document.getElementsByTagName("p") |
A tag is a word such as p, button, or h1. A class is a label beginning with.. An ID is a special name beginning with
in a CSS selector.
Parameters
| Parameter | Type | Required | Description | |---|---|---:|---| | id | String | Yes | The exact ID name, without #. | | selector | String | Yes | A CSS pattern, such as ".apple" or "button". | | className | String | Yes | A class name, without.. | | tagName | String | Yes | A tag name, such as "li". |
getElementById() and querySelector() return one element or null when nothing matches. The collection methods return a group that may be empty.
Code Example
`html Fruit Box
• Apple
• Banana
`
The browser first builds elements from the HTML. JavaScript then selects those elements and changes their text or style. CSS rules still control the page’s normal design.
Response Format
DOM selection does not return JSON. It returns an element or a group of elements.
json { "singleElement": "An element object, or null", "multipleElements": "A group of element objects, possibly empty" }
An element object represents a real page part, such as the heading or a list item.
Notes & Best Practices
• Place the script after the HTML, or wait until the page is ready. Otherwise, the element may not exist yet. - Use unique IDs. Two elements should not share the same ID. - Check for null before changing an element that might be missing. - Use textContent for plain text. It is safer than placing unknown text inside innerHTML.
Draw a small HTML tree with html, body, h1, and li boxes. Which box would querySelector("li") find first?
End of chapter one. 4 more chapters in the full book.
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What's inside: 5 chapters
- 1. HTML Trees and DOM Selection
- 2. DOM Updates and Interactive Events
- 3. Production DOM Interfaces
- 4. Arrow Function Essentials
- 5. Arrow Functions in Applications
About this book
"Javascript DOM And Arrow Functions" is a technical book by Anonymous with 5 chapters and approximately 2,234 words. JavaScript DOM manipulation and arrow functions from beginner concepts to professional frontend practice.
This book was created using Inkfluence AI, an AI-powered book generation platform that helps authors write, design, and publish complete books. It was made with the AI Documentation Generator.
Frequently Asked Questions
What is "Javascript DOM And Arrow Functions" about?
JavaScript DOM manipulation and arrow functions from beginner concepts to professional frontend practice
How many chapters are in "Javascript DOM And Arrow Functions"?
The book contains 5 chapters and approximately 2,234 words. Topics covered include HTML Trees and DOM Selection, DOM Updates and Interactive Events, Production DOM Interfaces, Arrow Function Essentials, and more.
Who wrote "Javascript DOM And Arrow Functions"?
This book was written by Anonymous and created using Inkfluence AI, an AI book generation platform that helps authors write, design, and publish books.
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