JavaScript Arrays
JavaScript
someandeverycheck whether elements pass a test and return true or false.
some asks whether at least one element passes.
every asks whether all of them do.
Example
javascript
const numbers = [1, 8, 3];
console.log(numbers.some(n => n > 5));
console.log(numbers.every(n => n > 5));The output is true then false.
Both return a boolean rather than an array.
some stops as soon as one element passes.
every stops as soon as one element fails.
Syntax
javascript
array.some(callback);
array.every(callback);The callback returns true or false for each element.
every is a natural fit for checking that all fields are filled.
Example
javascript
const fields = ["Ada", "London", "engineer"];
console.log(fields.every(f => f.length > 0));One empty field would make this false.
some answers the opposite question.
Example
javascript
const scores = [70, 45, 90];
console.log(scores.some(s => s < 50));The output is true, because one score is below 50.
This surprises people: every on an empty array is always true.
some on an empty array is always false.
Example
javascript
const empty = [];
console.log(empty.every(n => n > 100));
console.log(empty.some(n => n > 0));There is nothing to fail the test, so every passes.
Both work on arrays of objects in the same way.
Example
javascript
const users = [
{ name: "Ada", active: true },
{ name: "Alan", active: false }
];
console.log(users.some(u => u.active));
console.log(users.every(u => u.active));One active user makes some true but every false.
Neither method walks the whole array unless it has to.
Example
javascript
const numbers = [10, 1, 2, 3];
console.log(numbers.some(n => n > 5));The first element already answers the question, so the rest are skipped.
Complete Example
html
<!DOCTYPE html>
<html>
<head>
<title>JavaScript some and every</title>
</head>
<body>
<h1>JavaScript some and every</h1>
<p id="result"></p>
<script>
const scores = [70, 45, 90, 60];
document.getElementById("result").innerHTML =
"Anyone failed: " + scores.some(s => s < 50) +
"<br>Everyone passed: " + scores.every(s => s >= 50);
</script>
</body>
</html>Run the above example in the Try It Editor.
Try fixing the low score:
Change 45 to 55 and watch both answers flip.
some is true when at least one element passes.every is true when all elements pass.every on an empty array is true.some on an empty array is false.some and every answer yes-or-no questions about a list.
They are clearer than a loop with a flag variable.
Remember how they behave on empty arrays, which is a common interview question.