Array.prototype.some()

Summary: in this tutorial, you will learn how to use the JavaScript Array some() method to check if at least one element in the array passes a test.

Introduction to the JavaScript Array some() method #

Sometimes, you want to check if an array has at least one element that meets a specified condition.

For example, to check if the following array has at least one element less than 5:

let marks = [ 4, 5, 7, 9, 10, 3 ];Copy

…you typically use a for loop, like this:

let marks = [ 4, 5, 7, 9, 10, 3 ];

let lessThanFive = false;

for (let index = 0; index < marks.length; index++) {
    if (marks[index] < 5) {
        lessThanFive = true;
        break;
    }
}

console.log(lessThanFive);Copy

Output:

trueCopy

How it works:

• First, declare a flag variable lessThanFive and set its value to false.
• Second, iterate over the elements. If an element is less than 5, set the flag to true and immediately exit the loop using the break statement.

The code works as expected. However, it is quite verbose.

The Array type provides an instance method some() that allows you to test if an array has at least one element that meets a condition.

let marks = [ 4, 5, 7, 9, 10, 3 ];

lessThanFive = marks.some(function(e) {
    return e < 5;
});

console.log(lessThanFive);Copy

Output

trueCopy

The condition is implemented via a callback function passed into the some() method.

Now, the code is shorter. To make it more expressive, you can use the arrow function syntax in ES6:

let marks = [ 4, 5, 7, 9, 10, 3 ];

let lessThanFive = marks.some(e => e < 5);

console.log(lessThanFive);Copy

JavaScript Array some() syntax #

The following illustrates the syntax of the some() method:

arrayObject.some(callback[, thisArg]);Copy

The some() method accepts two arguments:

1) The callback argument #

The some() function executes the callback function once for each element in the array until it finds the one where the callback function returns a true. The some() method immediately returns true and doesn’t evaluate the remaining elements.

If no element causes the callback() to return true, the some() method returns false.

The callback function takes three arguments:

function callback(currentElement [[, currentIndex], array]){ // ...}Copy

• The currentElement is the current element being processed in the array.
• The currentIndex is the index of the current element being processed in the array.
• The array is array that some() was called upon.

2) The thisArg argument #

The thisArg argument is optional. If you pass the thisArg into the method, you can use the thisArg as the this value inside the callback function.

JavaScript Array some() examples #

Let’s take some more examples of using the some() method.

1) Check if an element exists in the array #

The following exists() function uses the some() method to check if a value exists in an array:

function exists(value, array) {
    return array.some(e => e === value);
}

let marks = [4, 5, 7, 9, 10, 2];

console.log(exists(4, marks));
console.log(exists(11, marks));Copy

Output:

true
falseCopy

2) Check if an array has one element that is in a range #

The following example shows how to check if any number in the marks array is in the range of (8, 10):

let marks = [4, 5, 7, 9, 10, 2];

const range = {
    min: 8,
    max: 10
};

let result = marks.some(function (e) {
    return e >= this.min && e <= this.max;
}, range);

console.log(result);Copy

Output:

trueCopy

How it works.

• First, define a range object with min and max properties.
• Second, call the some() method on the marks array object and pass the callback and range object. Because we pass the range object as the second argument (thisArg), we can reference it inside the callback via the this value.

Notice that if you use the arrow function in this example, the this value inside the callback function does not bind to the range object but the global object.

Caution: Empty arrays #

If you call the some() method on an empty array, the result is always false regardless of any condition. For example:

let result = [].some(e => e > 0);
console.log(result);

result = [].some(e => e <= 0);
console.log(result);Copy

Output:

false
falseCopy

Summary #

• Use the JavaScrip Array some() method to test if an array has at least one element that meets a condition.