FAQ: Objects - Looping Through Objects

FAQ JavaScript FAQ
#168

member is a variable containing a string, so in your example its similar to 'back-up'.

we can only uses keys to look up values in an object, keys itself do not contain information associated information about an object

#169

But back-up is a key that we use to look up it’s value battery. So if member is similar, then member.name should work just as ['back-up'].battery works above.

#170

it does:

for (const member in spaceship.crew) {
  console.log(spaceship.crew[member].name)
}

the loop simply means we get all the crew names instead of just a single one with a hard-coded key (like back-up)

#171

I’m sorry I know im going in circles but Im really trying to grasp this lol.

Each member in the loop references an object with a name property as I understand

for (const member in spaceship.crew) {
  console.log(member.name)
}

So doing this should work if we just wanted each crew member’s name. Is this logic wrong?

#172

member is not an object. If you attempt to log member and its type:

console.log(member, typeof member);

you will see member is a string, which we can use as key to look up information of spaceship crew

#173

My god I’m stupid, apologies I get it now

#174

Calling a function Looping Through Objects using the For … In

Hey guys, I don’t know if you already passed by this point, by I saw the functions inside of the object spaceship but each one with a different name, so came the question, how to call each function if they don’t follow a pattern like spaceship.crew.translator.name, so if I want to call each one like Shauna has the function powerFuel() I need to call spaceship.crew.translator.powerFuel(). However, as each one has a different function you can loop again Nested loops, ask the type of the object using typeof and call it using spaceship.crew[crewMember][details]()

I hope it will be usefull :wink:

for (let crewMember in spaceship.crew){
  console.log(`${crewMember} - ${spaceship.crew[crewMember].name}: ${spaceship.crew[crewMember].degree}`)

  console.log('---> Getting the type of the attribuites using typeof')
  for (details in spaceship.crew[crewMember]){
    console.log(`${details}: ${typeof(spaceship.crew[crewMember][details])}`)
    if (typeof(spaceship.crew[crewMember][details]) == 'function'){
      spaceship.crew[crewMember][details]()
    }
  }
  console.log('\n')
}
#176

I am having quite some challenges going through this class. Could someone help me understand better? Thanks!

I am a bit lost on why there is a difference in using the dot notation and bracket notation to access the degree property for each crew member.
Below is the code and error thrown.

for (let member in spaceship.crew) {
  console.log(spaceship.crew[member][degree]) // `ReferenceError: degree is not defined at Object.<anonymous> `
  console.log(spaceship.crew[member].degree) // this works
1 Like
#177

Documentation:

Bracket Notation
In the object[expression] syntax, the expression should evaluate to a string or Symbol that represents the property’s name. So, it can be any string literal, for example, including ‘1foo’, ‘!bar!’, or even ’ ’ (a space).

// As you said this works:
console.log(spaceship.crew[member].degree) 

// For bracket notation, you could do:
console.log(spaceship.crew[member]["degree"]); // This will work
console.log(spaceship["crew"][member]["degree"]);  // This will work

// This won't work because crew is not in quotes
console.log(spaceship[crew][member]["degree"]); 

// If you are wondering why quotes aren't needed for member,
// (let member in spaceship.crew) takes care of ensuring member is a string.
1 Like
#178

got cha! Thank you so much for the comprehensive response. Makes total sense!

1 Like
#179

In this exercise, the spaceship object contains multiple obejcts, which then contain more objects - a lot of nesting is going on.
Are the nested objects (inner objects) still properties of the outer objects? E.g.

let spaceship = {
engine: 'warp',
color: 'blue',  
crew: {
    captain: { 
      name: 'Lily', 
      degree: 'Computer Engineering', 
      cheerTeam() { console.log('You got this!') } 
    }
  }
};

Is crew a property of spaceship in the same way as color and engine?
Also, is name a property of captain in the same way that captain is a property of crew (is there a difference between properties of outer objects and those of nested objects)?

1 Like
#180

Short answer, no. Only ‘engine’, ‘color’ and ‘crew’ are properties of spaceship. The nested object is the value of the crew property.

#181

for (let crewMember in spaceship.crew) {
console.log(${crewMember}: ${spaceship.crew[crewMember].name})
}