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

• VLAZ: The answers seem to try and reinvent How do I check if an object has a specific property in JavaScript? 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."

Answer 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);

• Ben Aston: This will not shortcut if a mismatch is found?
• VLAZ: {alert: ""} will be counted as a failure
• RenaudC5: Note this wont work with {alert: false} either

Answer 2

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))

• VLAZ: {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.

Answer 3

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

• VLAZ: 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.

Answer 4

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