Web Development - HTML, CSS &… on Telegram: “const input = document.querySelector("input"); i…”

const input = document.querySelector("input");
input.addEventListener("keyup", () => {
    console.log("Typing...");
});

🖱️ 13. Mouse Events

Common mouse events: click, dblclick, mouseover, mouseout, mousemove

Example:

button.addEventListener("mouseover", () => {
    console.log("Mouse entered");
});

🚫 14. Prevent Default Behavior

Useful for forms and links.

form.addEventListener("submit", (event) => {
    event.preventDefault();
    console.log("Form Submitted");
});

🎯 15. Event Bubbling

When an event occurs, it moves from the child element to its parent.

Example:

parent.addEventListener("click", () => {
    console.log("Parent");
});
child.addEventListener("click", () => {
    console.log("Child");
});

Clicking the child prints:

Child

Parent

⚡ 16. Event Delegation

Instead of adding listeners to every child element, attach one listener to the parent.

document.getElementById("list")
.addEventListener("click", (event) => {
    if(event.target.tagName === "LI") {
        console.log(event.target.textContent);
    }
});

Benefits

Better performance, Less memory usage, Works for dynamically created elements

🛠️ 17. Mini Project Example

Button Click Counter

let count = 0;
const button = document.querySelector("button");
button.addEventListener("click", () => {
    count++;
    button.textContent = count;
});

Every click increases the displayed count.

⭐ Most Important Interview Topics

DOM Basics, querySelector(), textContent vs innerHTML, classList, Event Listeners, Event Bubbling, Event Delegation, event.target, preventDefault()

📝 Practice Questions

Easy

Change heading text, Change background color, Hide and show a button

Medium

Build a counter, Create a to-do list, Toggle dark mode

Advanced

Form validation, Image slider, Dynamic table, Infinite scrolling

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