key in dictionary javascript code example
Example 1: javascript does key exist
var person={"name":"Billy","age":20}
person.hasOwnProperty("name"); // true
person.hasOwnProperty("sex"); // false
Example 2: how to check if a key exists in an object javascript
!("key" in obj) // true if "key" doesn't exist in object
!"key" in obj // ERROR! Equivalent to "false in obj"
Example 3: js check if object key exists
var obj = { key: undefined };
obj["key"] !== undefined // false, but the key exists!
Example 4: js key in dict
"key" in obj // true, regardless of the actual value