Forms and Validation with JS
JavaScript can provide immediate form feedback. Use trim() to check whitespace-only values, but always validate again on the server.
JSON and Local Storage
JSON.stringify converts values into JSON text and JSON.parse reads it. localStorage persists small non-sensitive strings in a browser; never store passwords or secrets there.
Promises and Async/Await
Promises represent results that may arrive later. async/await makes asynchronous code easier to read; use try/catch to handle failures.
Fetch API Basics
fetch() makes HTTP requests. Check response.ok because HTTP error statuses do not automatically reject the promise, then parse JSON or text as needed.
JavaScript Final Project: To-do List
Combine DOM selection, event listeners, arrays, and localStorage to create a practical to-do list. Add items safely using textContent rather than inserting untrusted HTML.
Arrow Functions
Arrow functions offer concise syntax and capture this lexically. They work well for small callbacks but do not replace every regular function.
Arrays and Array Methods
Arrays store ordered collections. push adds an item, map transforms items, and filter selects matching items without changing the original array.
Objects and Properties
Objects group related data using named properties. Dot notation accesses common property names; bracket notation supports dynamic keys.
Selecting DOM Elements
The DOM represents a webpage as objects. querySelector selects the first matching element, while querySelectorAll returns a collection of matches.
Events and Event Listeners
Events report user interactions such as clicks and input. addEventListener attaches handlers without mixing JavaScript into HTML attributes.
Numbers and Math
JavaScript numbers use floating-point arithmetic, which can introduce small rounding differences. Use Math.round and related methods when appropriate.
Conditions with if and else
Conditions choose which block runs based on a boolean expression. Keep conditions readable and use strict comparisons where possible.