check if key exist in object in js code example

Example 1: javascript does key exist

var person={"name":"Billy","age":20}
person.hasOwnProperty("name"); // true
person.hasOwnProperty("sex"); // false

Example 2: check object has key javascript

Object.prototype.hasOwnProperty()

Example 3: js check if object key exists

var obj = { key: undefined };
obj["key"] !== undefined // false, but the key exists!