JS
(quick guide & examples)
var obj = { Name: "Jon", Email: "jon@doe.com", Gender: "Male" };
HAS OWN PROPERTY var exist = obj.hasOwnProperty("Name");
EXTRACT KEYS & CHECK var keys = Object.keys(obj); var exist = keys.includes("Email");
IN OPERATOR var exist = "Gender" in obj;
COMPARISON OPERATOR var exist = obj["Email"] !== undefined;
MANUAL LOOP & CHECK var check = "Name", exist = false; for (let key in obj) { if (key == check) { exist = true; break; } } console.log(exist);