JavaScript Array.every()

// function that checks whether
// the age is 18 or above
function checkAdult(age) {
    return age >= 18;
}

const ageArray = [34, 23, 20, 26, 12];

//checks if all the array elements
// pass the checkAdult() function
let check = ageArray.every(checkAdult);

// Output: false

every() Syntax

The syntax of the every() method is:

arr.every(callback(currentValue), thisArg)

Here, arr is an array.

every() Parameters

The every() method takes in:

• callback() - the function to test for each array element. It takes in:
  • currentValue - the current element being passed from the array.
• thisArg (optional) - value to use as this when executing callback(). By default, it is undefined.

every() Return Value

The every() method returns:

• true - if all the array elements pass the given test function (callback returns a truthy value).
• false - if any array element fails the given test function.

Example 1: Check if Array Elements Are Even

// function that checks whether all
// the array elements are even or not
function checkEven(num) {
    return num%2 === 0;
}

// create an array of numbers
const numbers = [2, 4, 6, 7, 8];

// use the every() method along with
// checkEven() on the numbers array
let check = numbers.every(checkEven); 

console.log(check)

// Output: false

In the above example, we have created the checkEven() function that checks whether a given number is even or not.

We then call the every() method on the numbers array. Since there is an odd number (7) in the array, we get false as an output.

Example 2: JavaScript every() With Arrow Function

let numbers = [ 1 , 2 , 3 , 4 , 5];

// use arrow function with every()
let result = numbers.every(element => element < 6);
console.log(result); 

// Output: true

In the above example, we have created the numbers array. Then, we call the every() method on that array.

Notice the arrow function element=> element < 6 inside the every() method. This function checks whether a given array element is less than 6 or not.

Since, all the elements in the numbers array are less than 6, we get true as an output.

Recommended Reading:

• JavaScript Array some()