I don't understand for...in fully. Can someone explain?

[h1lo]

https://www.codecademy.com/courses/introduction-to-javascript/lessons/objects/exercises/for-in
My code:

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

Why does this code output this:

captain : Lily
chief officer : Dan
medic : Clementine
translator : Shauna
Lily : Computer Engineering
Dan : Aerospace Engineering
Clementine : Physics
Shauna : Conservation Science

What does crewMember represent, and how was it used in the code above?

[harrjt]

Not seeing the list the for loop is iterating through, it appears the list is something like,

spaceship.crew = [captain, chief officer, medic, translator]

Think of the for (let crewMember in spaceship.crew) as a for each crewMember in the list spaceship.crew. The for loop iterates through each element in the list and executes the appropriate function as directed – in this case, logging the corresponding name and degree to the console.

[h1lo]

Here is the code I’m iterating through:

let spaceship = {
    crew: {
    captain: { 
        name: 'Lily', 
        degree: 'Computer Engineering', 
        cheerTeam() { console.log('You got this!') } 
        },
    'chief officer': { 
        name: 'Dan', 
        degree: 'Aerospace Engineering', 
        agree() { console.log('I agree, captain!') } 
        },
    medic: { 
        name: 'Clementine', 
        degree: 'Physics', 
        announce() { console.log(`Jets on!`) } },
    translator: {
        name: 'Shauna', 
        degree: 'Conservation Science', 
        powerFuel() { console.log('The tank is full!') } 
        }
    }
}; 

[mtf]

for..in enumerates an object by keys. crewMember is a key of the crew object.

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

[h1lo]

So each iteration crewMember becomes one of the 4 main keys in crew: [captain, chief officer, medic, translator], and so this code means: ${spaceship.crew[crewMember].name})
that it will go into crew, then crewMember will equal one of the 4 keys, and then you call .name on crewMember, so when you call this code:

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

It will print out

captain : Lily
chief officer : Dan
medic : Clementine
translator : Shauna

I think I get it now.