how to check if a key already exists in a dictionary node.js code example

Example 1: javascript hashtable contains key

if (obj.hasOwnProperty("key1")) {
  ...
}

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