check if key is present in javascript object code example

Example 1: how to check if object has key javascript

myObj.hasOwnProperty('key') // it checks object for particular key and not on prototype

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: check if a key exists in an object javascript

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

Example 4: js check if object key exists

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