HTML5 Constraint Validation API — JS Technical Interview Questions & Answers

Built-in required, pattern, min/max and checkValidity().

HTML5 Constraint Validation API

  • HTML5 Constraint Validation API (js) is a JS topic. In plain words you use it for let total = 0 in a cart script. Don’t start with a slogan — start with that picture.
  • Smallest example: let for change, const for fixed. Type it, run it, and say what you see. If you can do that from memory, you know HTML5 Constraint Validation API (js).
  • From the example next to this theory: Built-in required, pattern, min/max and checkValidity().
  • Trap: var leak / const reassign. Fix that before you talk about advanced JS.
  • Viva: what is HTML5 Constraint Validation API (js)? Then show let for change, const for fixed. Then name the trap.

Technical Interview Tip: What is HTML5 Constraint Validation API (js)? Show this: let for change, const for fixed. Trap: var leak / const reassign.

Code Examples for HTML5 Constraint Validation API

HTML5 Constraint Validation API — working example

function isEmail(value) {
  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(value);
}
function validate(form) {
  const errors = [];
  if (!form.email.trim()) errors.push("email required");
  else if (!isEmail(form.email)) errors.push("email invalid");
  if (form.age < 1 || form.age > 120) errors.push("age range");
  if ((form.password || "").length < 8) errors.push("password short");
  return errors;
}
console.log(validate({ email: "ada@example.com", age: 20, password: "secret123" }));
console.log(validate({ email: "", age: 0, password: "x" }));

HTML5 Constraint Validation API — client-side checks give fast feedback; still validate again on the server.

How to Explain HTML5 Constraint Validation API to an Interviewer

What is HTML5 Constraint Validation API (js)?

Used for let total = 0 a cart script Not just the heading

Give one small example of HTML5 Constraint Validation API (js).

let for change, const for fixed Built-in required, pattern, min/max and checkValidity()

What mistake do beginners make with HTML5 Constraint Validation API (js)?

var leak / const reassign Show the fix

Where do you use HTML5 Constraint Validation API (js)?

a cart script let total = 0