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JavaScript JavaScript Loops, Arrays and Objects Tracking Data Using Objects Using `for in` to Loop Through an Object's Properties

Daniel Fitzhugh
Daniel Fitzhugh
9,715 Points
Posted by Daniel Fitzhugh
Daniel Fitzhugh
9,715 Points

Can you use for/in loops on Objects that are contained within Arrays ?

Let's say that I wanted to loop through the first Object within this Array --- the entry for "Dave" --- and wanted to console.log() ALL of the property values, regardless of how long this particular Object might be.

var students = [ 
  { name: 'Dave', track: 'Front End Development', achievements: 158, points: 14730 },
  { name: 'Jody', track: 'iOS Development with Swift', achievements: '175', points: '16375' },
  { name: 'Jordan', track: 'PHP Development', achievements: '55', points: '2025' },
  { name: 'John', track: 'Learn WordPress', achievements: '40', points: '1950' },
  { name: 'Trish', track: 'Rails Development', achievements: '5', points: '350' }
];

If the Object was a standalone object not contained within an Array, I would use a for/in loop like this:

for ( prop in objectVariableName ) {
    console.log( objectVariableName[prop] );
}

But since Objects within an Array don't have variable names, I don't think a for/in loop would work. Am I wrong ?

Is there another way to do what I'm trying to do ?

2 Answers

Steven Parker
Steven Parker
229,670 Points
Steven Parker
Steven Parker
229,670 Points

You could give a specific object a name and do exactly what you have:

var objectVariableName = students[0];

Or, just substitute a specific index on the array for the object name:

for ( prop in students[0] ) {
    console.log( students[0][prop] );
}

You could also iterate through the entire array if you wanted to see all properties of all objects:

for (student of students) {
  for (prop in student) {
    console.log(student[prop]);
  }
}
Daniel Fitzhugh
Daniel Fitzhugh
9,715 Points
Daniel Fitzhugh
Daniel Fitzhugh
9,715 Points

Thanks Steven, great answer :)

We haven't learnt about "for/of" loops yet so I'll look into that.

Osaro Igbinovia
seal-mask
.a{fill-rule:evenodd;}techdegree
Osaro Igbinovia
Full Stack JavaScript Techdegree Student 15,928 Points
Osaro Igbinovia
.a{fill-rule:evenodd;}techdegree
Osaro Igbinovia
Full Stack JavaScript Techdegree Student 15,928 Points

Hi Daniel, you can still use your 'for in' loop. You just need to declare the specific object in the array you want to iterate over(which is the first object as you claimed). Take for example:

var students = [ 
  { name: 'Dave', track: 'Front End Development', achievements: 158, points: 14730 },
  { name: 'Jody', track: 'iOS Development with Swift', achievements: '175', points: '16375' },
  { name: 'Jordan', track: 'PHP Development', achievements: '55', points: '2025' },
  { name: 'John', track: 'Learn WordPress', achievements: '40', points: '1950' },
  { name: 'Trish', track: 'Rails Development', achievements: '5', points: '350' }
];

var firstObject = students[0];

for ( prop in firstObject) {
    console.log( firstObject[prop] );
}
Daniel Fitzhugh
Daniel Fitzhugh
9,715 Points
Daniel Fitzhugh
Daniel Fitzhugh
9,715 Points

Thanks Osaro, another great answer :)