JavaScript Array Methods - Some & Every

Today, I will tell you about .some() and .every(). Double knowledge. I don't use these as often as .map() or .filter() but they do come in quite handy in certain scenarios. I have grouped these methods together because they both return a Boolean value as a result, so it made sense (in my mind) to learn them together. Plus they are very short.

Array.prototype.some()

Just like the other methods I have talked about so far, .some() also take a function as its argument (a.k.a callback). The .some() method returns true for the first value/element in the array which passes the test and false otherwise.

I will use the typeof operator in my example, this operator returns a string telling you what the data type is.

Example:

let stoppingIndex;

const arrOfDataTypes = ["this is a string", 
  93, 
  false, 
  72n, 
  true,
  false,
  {
    name: "Tanwa", 
    hobby: ["coding", "gaming"]
  }
]

function callbackCheckBool(a) {
  return typeof a === 'boolean';
}

console.log(arrOfDataTypes.some( (element, index) => {
  stoppingIndex = index;
  return callbackCheckBool(element);
  }));
// true

console.log(stoppingIndex); // 2

console.log(arrOfDataTypes.some( element => typeof element === 'undefined'));
// false

In the above example, we wanted to check if there are some value/element in the array that are of the data type 'boolean', this return true because the array contains the element "false" which is a Boolean type at index 2 where the .some() method stopped. In the second .some() test, we check for data type of 'undefined', as the array does not have this type of value it returned false.

Array.prototype.every()

If you guess that .every() method returns true only when every value/element in the array passes the callback function test, then you would be correct! I think of .every() as the opposite to .some() as it will return the false as soon as one element fails the test.

Example:

const arrOfStrings = ["How", "long", "is", "a", "piece", "of", "string?", 1];

const arrOfTwos = [2,2,2,2,2];

console.log(arrOfStrings.every( element => typeof element === 'string')); // false

console.log(arrOfTwos.every( element => element === 2)); // true

I hope the example above is straight forward, we checked if every value/element in the array is of the type 'string' but this return false because of the sneaky number 1 at the end! And in the second .every() test, it returns true as all the element passed the test.

Summary

The .some() method checks for first value/element in the array that passes the callback function test and returns true and if it does not find any that passes the test it returns false. While the .every() method checks for the first value/element in the array that fails the callback function test and returns false or it returns true if all the value passes the test.

If you made it this far, thank you for reading, and as always please leave comment and feedback if I have misunderstood anything.