Checking if all array values are smaller than a limit using JavaScript

Problem

We are required to write a JavaScript function that takes in an array of numbers and a number. We should return true if all the numbers in the array are smaller than the number given as second argument, false otherwise.

Using Array.every() Method

The Array.every() method tests whether all elements in the array pass the test implemented by the provided function. It returns true if all elements satisfy the condition, false otherwise.

Example 1: All Values Smaller

Following is the code −

const arr = [5, 34, 23, 14, 78, 45, 78];
const limit = 99;
const checkEvery = (arr = [], limit = 1) => {
    const allSmaller = arr.every(el => {
        return el < limit;
    });
    return allSmaller;
};
console.log(checkEvery(arr, limit));

true

Example 2: Some Values Larger

Let's test with a scenario where some values exceed the limit:

const arr2 = [5, 34, 23, 14, 105, 45, 78];
const limit2 = 99;
console.log(checkEvery(arr2, limit2));

false

Simplified Version

We can simplify the function by directly returning the result of every():

const checkEverySimple = (arr = [], limit = 1) => {
    return arr.every(el => el < limit);
};

// Testing with different arrays
console.log(checkEverySimple([10, 20, 30], 40));  // true
console.log(checkEverySimple([10, 20, 50], 40));  // false
console.log(checkEverySimple([], 10));            // true (empty array)

true
false
true

Key Points

• Array.every() returns true for empty arrays (vacuous truth)
• The method stops checking as soon as it finds the first element that doesn't satisfy the condition
• All elements must satisfy the condition for the method to return true

Conclusion

Array.every() provides an elegant solution for checking if all array elements meet a specific condition. It's efficient because it short-circuits on the first failing element.