Read input values and validate forms.
✍️ 3 exercises + code challenge in this lessonJavaScript can read and validate form data before it is sent.
input.value (always a string).submit event and call event.preventDefault() to stop the page from reloading.new FormData(form) collects every named field.input.checkValidity() uses the HTML validation rules (required, type, pattern).Mastering JavaScript Forms helps you write clean and reliable JavaScript code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.
<form id="signup">
<input name="name" placeholder="Name" required><br><br>
<input name="email" type="email" placeholder="Email" required><br><br>
<input name="password" type="password" placeholder="Password (8+ chars)"><br><br>
<button>Sign up</button>
</form>
<p id="msg"></p>
<script>
document.getElementById("signup").addEventListener("submit", (e) => {
e.preventDefault();
const data = Object.fromEntries(new FormData(e.target));
const msg = document.getElementById("msg");
if (data.password.length < 8) {
msg.style.color = "#E34F26";
msg.textContent = "Password must be at least 8 characters.";
return;
}
msg.style.color = "#14B8A6";
msg.textContent = `Welcome, ${data.name}! (${data.email})`;
});
</script>Check what you learned in “JavaScript Forms”.
Stop the form from reloading the page.
form.addEventListener("submit", (e) => {
e.();
});
What type is input.value always?
Read the value of the input with id "name" and show it in #out as "Hello, <value>". (Run it on load.)
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