Javascript: How to check for certain items in an array

Question

How can I check if the items in an array like:

var dayPartsArr = ['PT','WDM','WDD','EF','WKE'];

are also the keys in an object like:

 var dayPartsMap = {
   'PT': 'PRIME TIME',
   'WDM': 'WEEKDAY MORNING',
   'WDD': 'WEEKDAY DAYTIME',
   'EF': 'EARLY FRINGE',
   'WKE': 'WEEKEND DAYTIME'
 };

Keep in mind the order of the dayPartsArr should not matter. So if

var dayPartsArr = ['WKE','PT','WDM','WDD','EF'];

I still want to be able to use dayPartsMap to check if each item in dayPartsArr is a key in dayPartsMap

pxljoy · Answer 1 · 2018-07-12T00:59:10.223

Ignoring Order

Ignoring order, we can take the input array and compare it to the keys like so:

var dayPartsArr = ['WDM','PT','WDD','EF','WKE']; //out of order

var dayPartsMap = {
  'PT': 'PRIME TIME',
  'WDM': 'WEEKDAY MORNING',
  'WDD': 'WEEKDAY DAYTIME',
  'EF': 'EARLY FRINGE',
  'WKE': 'WEEKEND DAYTIME'
};

dayPartsArr.every(item => ~Object.keys(dayPartsMap).indexOf(item)); // true

// Compare against an array with a missing key
dayPartsArr = ['WDM','PT','FAKE', 'WDD','EF','WKE'];

dayPartsArr.every(item => ~Object.keys(dayPartsMap).indexOf(item)); // false

Note the ~ is the bitwise NOT operator, it helps with indexOf

Previous Answer

You can convert the Object's keys to an array and compare that array, like so:

For more information on Object.keys, check MDN here.

var dayPartsArr = ['PT','WDM','WDD','EF','WKE'];

var dayPartsMap = {
  'PT': 'PRIME TIME',
  'WDM': 'WEEKDAY MORNING',
  'WDD': 'WEEKDAY DAYTIME',
  'EF': 'EARLY FRINGE',
  'WKE': 'WEEKEND DAYTIME'
};

// Create the comparison function...
function arraysIdentical(a, b) {
   var i = a.length;
   if (i != b.length) return false;
   while (i--) {
       if (a[i] !== b[i]) return false;
   }
       return true;
};

/// compare!
arraysIdentical(dayPartsArr, Object.keys(dayPartsMap)); // true

arraysIdentical originally suggested by Tim Down

What about if the items in dayPartsArr were in a different order? would this still work? See my revised question above — NewToJS, Jul 11 '18 at 14:26
@NewToJS Note this also works if the `dayPartsArr` contains duplicates. — pxljoy, Jul 12 '18 at 01:01

score 0 · Answer 2 · answered Jul 11 '18 at 06:05

We can use every and filter to solve the issue.

Ref:

var dayPartsArr = ['PT','WDM','WDD','EF','WKE'];
var dayPartsMap = {
   'PT': 'PRIME TIME',
   'WDM': 'WEEKDAY MORNING',
   'WDD': 'WEEKDAY DAYTIME',
   'EF': 'EARLY FRINGE',
   'WKE': 'WEEKEND DAYTIME', 
};

// > 1 for WKE
// var dayPartsArr = ['PT','WDM','WDD','EF','WKE', 'WKE'];

const check = Object.keys(dayPartsMap).every(key =>   dayPartsArr.filter(day => day === key).length === 1);

console.log(check);

Leonid Pyrlia · Answer 3 · 2018-07-11T08:23:58.563

You can use Array.prototype.every to check if all items of dayPartsArr are present in dayPartsMap keys:

var dayPartsArr = ['PT','WDM','WDD','EF','WKE'];

var dayPartsMap = { 'PT': 'PRIME TIME', 'WDM': 'WEEKDAY MORNING', 'WDD': 'WEEKDAY DAYTIME', 'EF': 'EARLY FRINGE', 'WKE': 'WEEKEND DAYTIME' };

var objKeys = Object.keys(dayPartsMap);
var result = dayPartsArr.every(day => objKeys.includes(day));

console.log(result);

Javascript: How to check for certain items in an array

3 Answers3

Ignoring Order

Previous Answer