Null Operators

app.js

console.log(null || 'default value'); // 'default value'
  console.log(undefined || 'default value'); // 'default value'
  console.log(false || 'default value'); // 'default value'
  console.log('' || 'default value'); // 'default value'
  console.log(0 || 'default value'); // 'default value'
  console.log(NaN || 'default value'); // 'default value'
  console.log('Hello' || 'default value'); // 'Hello'

  console.log(null || 100); // 100
  console.log(undefined || 100); // 100
  console.log(false || 100); // 100
  console.log('' || 100); // 100
  console.log(0 || 100); // 100

  console.log(null ?? 'default value'); // 'default value'
  console.log(undefined ?? 'default value'); // 'default value'
  console.log(false ?? 'default value'); // false
  console.log('' ?? 'default value'); // ''
  console.log(0 ?? 'default value'); // 0
  console.log(0 ?? 100); // 0
  console.log(10 ?? 100); // 10

  const jamie = {
    name: 'Jamie',
    cat: {
      name: 'Pixel',
      toys: ['floppy fish'],
    },
  };

  console.log(jamie.cat.name); // Jamie
  console.log(jamie.cat.toys[0]); // floppy fist

  console.log(jamie.dog); // undefined
  console.log(jamie.dog.name); // error - cannot react property of undefined

  console.log(jamie.getAddress); // undefined
  console.log(jamie.getAddress()); // Error

  console.log(jamie.cat.hobbies); // undefined
  console.log(jamie.cat.hobbies[0]); // Error

  let john = {
    name: 'John',
    address: {
      country: 'France',
    },
  };

  let jane = {
    name: 'Jane',
  };

  function logPerson(person) {
    console.log('Name', person.name);
    console.log('Country', person?.address?.country);
  }

  logPerson(john); // Name John, Country France
  logPerson(jane); // Name Jane, Country undefined

  console.log(jamie.dog); // undefined
  console.log(jamie.dog?.name); // undefined

  console.log(jamie.getAddress); // undefined
  console.log(jamie.getAddress?.()); // undefined

  console.log(jamie.cat.hobbies); // undefined
  console.log(jamie.cat.hobbies?.[0]); // undefined