Difference between JavaScript Array every and some

Question

I see both return true or false upon given tests.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every

What should be the right case to use them both together ?

Test code:

function checkUsersValid(goodUsers) {
  return function allUsersValid(submittedUsers) {
    //Im testing arrays here
    return submittedUsers.every(function isBigEnough(element, index, array) {
	  return goodUsers.some(function (el, i, arr) {
	  	return element.id == el.id;
	  });
	});
  };
}

var goodUsers = [
      { id: 1 },
      { id: 2 },
      { id: 3 }
    ];
    
var testAllValid = checkUsersValid(goodUsers);

testAllValid([
      { id: 2 },
      { id: 1 }
    ]);

Answer 1

(If you know C# LINQ , it's like Any vs All)

• some will return true if any predicate is true

• every will return true if all predicate is true

Where predicate means function that returns bool ( true/false) for each element

every returns on first false.
some returns on first true

Answer 2

some is analogue to logical or
every is analogue to logical and

logically every implies some, but not in reverse

try this:

var identity = function(x){return x}
console.log([true, true].some(identity))//true
console.log([true, true].every(identity))//true
console.log([true, false].some(identity))//true
console.log([true, false].every(identity))//false
console.log([false, false].some(identity))//false
console.log([false, false].every(identity))//false
console.log([undefined, true].some(identity))//true
console.log([undefined, true].every(identity))//false
console.log([undefined, false].some(identity))//false
console.log([undefined, false].every(identity))//false
console.log([undefined, undefined].some(identity))//false
console.log([undefined, undefined].every(identity))//false

Answer 3

The documentation answers your question...

The some() method tests whether some element in the array passes the test implemented by the provided function.

The every() method tests whether all elements in the array pass the test implemented by the provided function.

So you will use them, according if you want to test some elements or every elements.

If every() returns true then some() returns true.

but

If some() returns true then we cannot conclude anything about the result of every().