What is the difference between null and undefined in JavaScript?

PrintLog.js

null === undefined // false
null !== undefined // true

// Example
function PrintLog(str = 'Test') {
    console.log(str);
}
PrintLog(); // Prints 'Test'
PrintLog("Hello World"); // Prints 'Hello World'
// But the surprise is here,
PrintLog(undefined); // Prints 'Test'
PrintLog(null); // Prints 'null'