Answers for "typecript check if a key exists"

javascript does key exist

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

Checking if a key exists in a JavaScript object?

5003

Checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined?

var obj = { key: undefined };
console.log(obj["key"] !== undefined); // false, but the key exists!