Check for a key inside In array of objects

Question

I am trying to find the best way to check whether an object key is present inside multiple objects present in an array which will provide a boolean as output [{alert:hi},{alert:bye},{}]

From the above example basically what I am trying to achieve is if any one object is missing the alert object key the output should be as false or anything

The answers seem to try and reinvent [How do I check if an object has a specific property in JavaScript?](https://stackoverflow.com/q/135448) which has been on the site for more than a dozen years? Note the top answer by John Resig (author of jQuery): "*I'm really confused by the answers that have been given - most of them are just outright incorrect. Of course you can have object properties that have undefined, null, or false values.*" — VLAZ, Jun 07 '22 at 07:48

Jax-p · Accepted Answer · 2022-06-07T07:47:11.547

1

You can iterate your array with every(). Something like this:

const objects = [{alert:'hi'},{alert:'bye'},{}];
const every = objects.every(obj => obj.hasOwnProperty('alert'));
console.log(every);

edited Jun 07 '22 at 07:47

answered Jun 07 '22 at 07:38

Jax-p

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This will not shortcut if a mismatch is found? – Ben Aston Jun 07 '22 at 07:40
`{alert: ""}` will be counted as a failure – VLAZ Jun 07 '22 at 07:41
Note this wont work with `{alert: false}` either – RenaudC5 Jun 07 '22 at 07:41

score 1 · Answer 2 · answered Jun 07 '22 at 07:40

1

You can use the Array#some method and check if at least one element is undefined

const isAlertMissing = (array) => array.some(elem => elem.alert === undefined)

const objs1 = [{alert: "foo"},{alert: "foo"},{}]
const objs2 = [{alert: "foo"},{alert: "foo"}]

console.log(isAlertMissing(objs1))
console.log(isAlertMissing(objs2))

answered Jun 07 '22 at 07:40

RenaudC5

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`{alert: undefined}` means *the key is present* but the value of it is set to `undefined`. That's different to `{}` where the key is *not* present. – VLAZ Jun 07 '22 at 07:42

Nick Vu · Answer 3 · 2022-06-07T07:55:00.477

1

You can use every to check all items and some with Object.keys for finding a key in the inner objects.

const data = [{alert:"hi"},{alert:"bye"},{}]
const result = data.every(item => Object.keys(item).some(key => key === "alert"));

console.log(result) //false

EDIT

some with Object.keys is kind of roundabout, so we can use hasOwnProperty instead.

const data = [{alert:"hi"},{alert:"bye"},{}]
const result = data.every(item => item.hasOwnProperty("alert"));

console.log(result) //false

edited Jun 07 '22 at 07:55

answered Jun 07 '22 at 07:42

Nick Vu

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2

`Object.key()` is extremely roundabout way to check for a key. Moreover, it only works on own keys which rarely matters but might still be a consideration. – VLAZ Jun 07 '22 at 07:43

score 0 · Answer 4 · answered Jun 07 '22 at 07:53

Array#some will succeed as soon a match is found, making it more efficient than Array#every.

const test = (data, propName) => 
  !(data.some((el) => !el.hasOwnProperty(propName)))

const data1 = [ {alert:'hi'}, {alert:'bye'}, {}]
const data2 = [ {alert:'hi'}, {alert:'bye'}]

console.log(test(data1, 'alert')) // false
console.log(test(data2, 'alert')) // true

Or:

const test = (data, propName) => {  
  for(let el of data) {
    if(!el.hasOwnProperty(propName)) 
      return false 
  }

  return true
}

const data1 = [ {alert:'hi'}, {alert:'bye'}, {}]
const data2 = [ {alert:'hi'}, {alert:'bye'}]

console.log(test(data1, 'alert')) // false
console.log(test(data2, 'alert')) // true

Check for a key inside In array of objects

4 Answers4