遍历对象属性/键

Question

I'm just starting to learn coding, and i came across this question that i could not understand.

"The second function we'll add will be called search, and it will take a first name as an argument. It will try to match the first name it receives to any of the first names in our friends contact list. If it finds a match, it will log our friend's contact information (firstName, lastName, number, address) to the console."

variables are define as follows :

var friends = {}; 
friends.bill = { 
  firstName: "Bill", 
  lastName: "gates", 
  number: "1234567", 
  address: ['bishan','starbucks', 'centertable'] 
}; 

friends.steve = { 
  firstName: "Steve", 
  lastName: "jobs", 
  number: "987654", 
  address: ['orchird', 'ikoma', 'ga'] 
};

the answer is as follows :

var search = function(name) {
    for(var key in friends) {
        if(friends[key].firstName === name) {
            console.log(friends[key]);
            return friends[key];
        }
    }
};

could someone better explain how did the var "key" came about ? and why can't i just input friends.firstName === name, console.log(friends.name), return friends.name ??

would appreciate if someone could explain thank you.

Answer 1

From OP's comment:

var friends = {}; 

friends.bill = { 
  firstName: "Bill", 
  lastName: "gates", 
  number: "1234567", 
  address: ['bishan','starbucks', 'centertable'] 
}; 

friends.steve = { 
  firstName: "Steve", 
  lastName: "jobs", 
  number: "987654", 
  address: ['orchird', 'ikoma', 'ga'] 
};

friends is a nested object which can also be represented like so:

friends = {
  bill: { 
      firstName: "Bill", 
      lastName: "gates", 
      number: "1234567", 
      address: ['bishan','starbucks', 'centertable'] 
  },
  steve: { 
      firstName: "Steve", 
      lastName: "jobs", 
      number: "987654", 
      address: ['orchird', 'ikoma', 'ga'] 
  }
}

The for..in loop iterates over all keys in the friends object, with the variable key in your case.

why can't i just input friends.firstName === name, console.log(friends.name), return friends.name ??

Because, to do that, you need to have firstName or name as a property in friends . Since those properties are nested inside ( name is not event inside the nested objects), there was a for..in loop used.

Answer 2

You have an object friends that has 2 properties bill and steve (those are the keys). Calling friends.bill will return you an object (the value) with firstname, lastname, number, address . You need to iterate all the properties of your object friends to find the one you need

You can use Object.values(obj)

 var firstNameInput = "Steve"; var friends = {}; friends.bill = { firstName: "Bill", lastName: "gates", number: "1234567", address: ['bishan','starbucks', 'centertable'] }; friends.steve = { firstName: "Steve", lastName: "jobs", number: "987654", address: ['orchird', 'ikoma', 'ga'] }; //Iterates all the friends Object.values(friends).forEach(function(f){ //Compare the property "firstname" with the input if(f.firstName === firstNameInput){ //Friend found console.log(f); return; } });