All Must Match
every returns true only if all elements pass the test.
It stops early when it finds a failing element.
JavaScript Tutorial
JavaScript every()
every checks whether all elements in an array satisfy a condition.
It returns true only if every item passes.
Why We Need It
Many validation tasks require confirming all items are valid.
every expresses this clearly and stops early for efficiency.
Syntax
array.every((value, index, array) => condition)Basic Example
1. All even
const nums = [2, 4, 6];
const allEven = nums.every((n) => n % 2 === 0);
console.log(allEven);All items match, so result is true.
Real World Example
2. Not all match
const nums = [2, 3, 4];
const allEven = nums.every((n) => n % 2 === 0);
console.log(allEven);One item fails, so result is false.
Multiple Use Cases
Validation
every is great for validation rules like all fields filled.
If you need any match, use some instead.
Empty Arrays
every on an empty array returns true by definition.
Handle this case if it matters.
More Examples
3. Validation
const fields = ["name", "email"];
const valid = fields.every((f) => f.length > 0);
console.log(valid);Use every to validate all fields.
4. Objects
const users = [{ active: true }, { active: true }];
const allActive = users.every((u) => u.active);
console.log(allActive);Works with arrays of objects too.
Comparison
Without
let allValid = true;
for (const n of nums) {
if (n <= 0) {
allValid = false;
break;
}
}With
const allValid = nums.every((n) => n > 0);Common Mistakes and Fixes
Using every for any match
Use some when you need at least one match.
Forgetting empty arrays return true
Check array length when needed.
Expecting every to return items
every returns a boolean, not items.
Interview Questions
What does every return on empty arrays?
True.
When should you use every?
When all elements must satisfy a condition.
How is every different from some?
every requires all; some requires any.
Practice Problem
Practice: Check if all scores are 50 or above.
const scores = [70, 55, 40];
// TODO: check all >= 50
One Possible Solution
const scores = [70, 55, 40];
const ok = scores.every((s) => s >= 50);
console.log(ok);Frequently Asked Questions
What does every return?
A boolean indicating if all items pass the test.
Does every stop early?
Yes, it stops when a failure is found.
What about empty arrays?
every returns true for empty arrays.
Try It Yourself
Try arrays with mixed values to see results.