JavaScript There are more than one method to check it. First, we can use hasOwnProperty method. let object = {"one": 2, "tree": "floor", 5: "socks"}; console.log(object.hasOwnProperty("tree")); // true console.log(object.hasOwnProperty(4)); // false // (Not in the object) We'll expect boolean output. Second, we can use in operator. let object = {"one": 2, "tree": "floor", 5: "socks"}; console.log("tree" in object); // true console.log(4 in object); // false // (Not in the object) We'll expect boolean output. Third, straight away access the property name we need to find out. let object = {"one": 2, "tree": "floor", 5: "socks"}; console.log(object.tree); // "floor" // (Value of that property) console.log(object[4]); // undefined // (Undefined value from that given property name in the object) We'll exp...