Answers for "javascript if dict has key"

check if a key exists in an object javascript

"key" in obj // true, regardless of the actual value

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!