Welcome to the MDN Learning Area. This set of articles aims to provide complete beginners to web development with all they need to start coding simple websites.
The aim of this area of MDN is not to take you from “beginner” to “expert” but to take you from “beginner” to “comfortable”. From there you should be able to start making your own way, learning from the rest of MDN and other intermediate to advanced resources that assume a lot of previous knowledge.
If you are a complete beginner, web development can be challenging — we will hold your hand and provide enough detail for you to feel comfortable and learn the topics properly. You should feel at home whether you are a student learning web development (on your own or as part of a class), a teacher looking for class materials, a hobbyist, or someone who just wants to understand more about how web technologies work.
instanceofcheck what a value is and where it comes from. As we have seen, both operators have serious limitations.
In contrast, duck typing checks what a value does and provides. After all, you are not interested in the type of a value, you are interested in what you can do with the value.
Duck typing would ask instead: What does the function do with the value? Then check whether the value fulfills the needs, and be done with it.
This check is not as strict as
instanceof, and that is an advantage. A function that does not assert types but object capabilities is more flexible.
Array.prototypebut walk and talk like arrays: Arguments, HTMLCollection and NodeList. A function that uses duck typing is able to support all array-like types.
I recently embarked on improving the client-side form validation for a client. There were about 400 lines of form validation code stuffed inside a 1000 line
form_helper.js. I looked for lightweight form validation scripts but after some hemming and hawing I decided to try my hand (again) at native HTML5 Form Validation.
If you’ve ever experimented with HTML5 Form Validation, you’ve probably been disappointed. The out-of-box experience isn’t quite what you want. Adding the
requiredattribute to inputs works wonderfully. However the styling portion with
input:invalidsorta sucks because empty inputs are trigger the
:invalidstate, even before the user has interacted with the page.
I finally sat down and spent a couple days trying to make HTML5 Form Validation work the way I want it. I had the following goals:
- Leverage browser-level feedback, free focus management and accessible labelling
- Only validate inputs on submit
- Styling with
With this wishlist in hand, I set off and found a solution that works with only 6 lines of code.
If you ever wanted a mini-cheat sheet for what every part of a CSS rule is called, here it is:
- The whole thing is a ruleset.
- The curly braces and everything inside is a declaration block.
- The bit before the opening curly brace is a selector.
- Each key/value pair, as separated by a colon and ending in a semicolon, is a declaration.
- In those key/value pairs, the key is a property (or property name), and the value is a value (or property value).
This looks like a great resource for anyone wanting to get into web development and design.
This is a pretty neat interactive web development/design demo that shows how the different layers are applied, step by step, to create a web page.