Javascript in 100 bits

Course by zooboole,

Last Updated on 2025-01-28 08:04:00

Lesson 40 - JavaScript Array Method – every()

The every() method checks whether all elements in an array satisfy a given condition. It returns true if all elements pass the test; otherwise, it returns false.

Explanation

  • It runs a callback function on every element in the array.
  • If all elements satisfy the condition, it returns true.
  • If at least one element fails, it returns false.
  • It does not modify the original array.

Syntax

let result = array.every((element, index, array) => {
    return condition;
});
  • element: The current item being processed.
  • index (optional): The index of the current element.
  • array (optional): The array being processed.

Example 1: Checking If All Numbers Are Positive

let numbers = [2, 4, 6, 8];

let allPositive = numbers.every(num => num > 0);

console.log(allPositive); // Output: true
  • All numbers are positive, so it returns true.

Example 2: Checking If All Words Are Shorter Than 6 Letters

let words = ["apple", "banana", "kiwi"];

let allShortWords = words.every(word => word.length < 6);

console.log(allShortWords); // Output: false
  • "banana" is longer than 6 letters, so it returns false.

Example 3: Checking an Empty Array

let emptyArray = [];

let checkEmpty = emptyArray.every(num => num > 0);

console.log(checkEmpty); // Output: true
  • The method returns true for an empty array because there are no elements to check.

Try Your Hand

Steps:

  1. Create a File:

    • Name it lesson40-every.html.

  2. Write the Code:

    • Copy the following:

      <!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Lesson 42 - every() Method</title>
</head>
<body>
<h2>Checking If All Numbers Are Even</h2>
<p id="result"></p>

<script>
   let numbers = [2, 4, 6, 8, 10];

   let allEven = numbers.every(num => num % 2 === 0);

   document.getElementById("result").textContent = "All numbers are even: " + allEven;
</script>
</body>
</html>

  3. Save the File.

  4. Open it in a Browser to Check If All Numbers Are Even.

Experiment

  1. Check if all numbers in an array are greater than 10.
  2. Verify if all elements in an array of booleans are true.
  3. Ensure all students in an array have passed an exam (e.g., score >= 50).

Key Takeaways

  • every() checks all elements against a condition.
  • If all match, it returns true; otherwise, it returns false.
  • It stops checking as soon as it finds a failure.
  • Returns true for an empty array.