Javascript: Loop Through Object By Number Index Rather Than Key-Value

Question

While looping through an object is simple using for(key in object), I'd like to access an object via an index (like an array) rather than its value.

I have a "days of the week" object composed of:

days: { sunday: "N", monday: "Y", tuesday: "N", wednesday: "Y", 
thursday: "N", friday: "Y", saturday: "N" }

I want to use a for-loop which cycles through the seven days of the week (0-6) and checks whether the object is "Y" or "N" for that day (checking the "days" object for the value at key 0 (sunday), 1 (monday), 2, 3, etc.)

for (var i = 0; i < 7; i++) { }

My problem could be solved with a bunch of if statements if i == 0 { //check sunday } else if i == 1 { //check monday } or manipulating my object into multiple arrays and going from there, however neither of these are very elegant. Is there a way to loop through the days object and access each value by a key (0 for first, 1 for second, etc.)?

Order cannot be guaranteed. You could use Object.keys(daysObject) for collecting all the day properties in an array, and after that you could iterate over it. Again, I am saying order cannot be guaranteed. — Rajaprabhu Aravindasamy
– Rajaprabhu Aravindasamy, Commented Dec 8, 2017 at 19:23
Javascript objects are maps, which by definition, are not indexed. — Jim Cote
– Jim Cote, Commented Dec 8, 2017 at 19:24
@NinaScholz That's what I'm working on using at the moment. I wasn't sure if there was an elegant way to do it as I described, and am hoping there still is - but for now, I'll be manipulating it into an array. — T. Tenner
– T. Tenner, Commented Dec 8, 2017 at 19:39

janos · Accepted Answer · 2017-12-08 19:42:14Z

1

To iterate over the properties of an object in a consistent order, you have no choice but to use an array of the property names, for example:

var daysList = [ 'sunday', 'monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday' ];

And then you can iterate over the array of names:

for (let i = 0; i < daysList.length; i++) {
    let day = daysList[i];
    // do what you need with days[day]
}

answered Dec 8, 2017 at 19:42

janos

126k31 gold badges242 silver badges253 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

T. Tenner Over a year ago

It does indeed seem that there is no way to do what I wanted in the manner I desired.

ewizard Over a year ago

not quite as elegant as this i guess...but another way is Map

ewizard · Accepted Answer · 2017-12-08 20:25:52Z

1

You can use Map - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map

const days = { sunday: "N", monday: "Y", tuesday: "N", wednesday: "Y", 
thursday: "N", friday: "Y", saturday: "N" }

const map = new Map(Object.entries(days));
var mapIter = map.entries();

x = 0;
while(x < Object.keys(days).length) {
  let next = mapIter.next().value
  if(next[1] == 'Y') {
    console.log(next[0] + " is Y");
  }
  else if(next[1] == 'N') {
    console.log(next[0] + " is N");
  }
  x++;
}

answered Dec 8, 2017 at 20:25

ewizard

2,8924 gold badges56 silver badges113 bronze badges

3 Comments

Arjan Over a year ago

Object.entries(days) does NOT guarantee the order: "The Object.entries() method returns an array of a given object's own enumerable property [key, value] pairs, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well)."

ewizard Over a year ago

seems like it maintains order to me...look at the code snippet

Arjan Over a year ago

One code snippet does not prove it, sorry. The order of for...in is NOT determined in JavaScript, even though many browsers preserve the order: "A for...in loop iterates over the properties of an object in an arbitrary order".

Collectives™ on Stack Overflow

Javascript: Loop Through Object By Number Index Rather Than Key-Value

2 Answers 2

2 Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related