Filter an Array to only Numbers in JavaScript

# Filter an Array to only Numbers in JavaScript

To filter an array to only numbers:

1. Use the Array.filter() method to iterate over the array.
2. Use the typeof operator to check if each element is a number.
3. The filter method will return a new array containing the numbers of the original array.

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const arr = [1, 'test', 3, null];

const onlyNumbers = arr.filter(
  element => typeof element === 'number'
);
console.log(onlyNumbers); // 👉️ [1, 3]

The function we passed to the Array.filter method gets called with each element in the array.

The filter() method returns a new array that only contains the elements that meet the condition.

On each iteration, we check if the element has a type of number using the typeof operator.

All the elements that meet the condition (have a type of number) will get added to the new array.

# Dealing with string elements that are valid numbers

If you have an array of strings that might be valid numbers, pass the Number object to the filter() method.

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const arr = ['1', 'test', '3', 5];
const validNumbers = arr.filter(Number);

// 👇️ ['1', '3', 5]
console.log(validNumbers);

We used the filter method to iterate over the array. On each iteration, we convert the element to a number and return the result.

Note that if a value of 0 is passed to the number object, it wouldn't get included in the new array because 0 is a falsy value.

The falsy values in JavaScript are: null, undefined, false, 0, "" (empty string), NaN (not a number).

You can explicitly check for 0 to have zeros pass the test as well.

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const arr = ['1', 'test', '3', 5, 0];

const validNumbers = arr.filter(element => {
  return element === 0 || Number(element);
});

// 👇️ [ '1', '3', 5, 0 ]
console.log(validNumbers);

We used the logical OR (||) operator, so for the element to be included in the new array, either condition has to be met.

# Converting the results to numbers

The filter method doesn't convert the strings in the array to numbers, it simply returns the elements that meet the condition.

You can call the map() method on the filtered array to get an array of numbers.

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const arr = ['1', 'test', '3', 5];
const validNumbers = arr.filter(Number);

// 👇️ ['1', '3', 5]
console.log(validNumbers);

const toNumbers = validNumbers.map(Number);
console.log(toNumbers); // 👉️ [1, 3, 5]

The function we passed to the Array.map() method gets called with each element in the array.

The map() method returns a new array containing the values returned from the callback function.

# Filter an Array to only Integers in JavaScript

To filter an array to only integers:

1. Use the Array.filter() method to iterate over the array.
2. Use the Number.isInteger() method to check if each element is an integer.
3. The filter() method will return a new array containing only the integers.

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const arr = [1.1, 6, 'test', undefined, 5, 14, 0];

const validNumbers = arr.filter(Number.isInteger);

// 👇️ [ 6, 5, 14, 0 ]
console.log(validNumbers);

The Number.isInteger() method returns true if the provided value is an integer and false otherwise.

Here are some examples of using the Number.isInteger() method directly.

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console.log(Number.isInteger(1)); // 👉️ true
console.log(Number.isInteger(1.5)); // 👉️ false
console.log(Number.isInteger('1')); // 👉️ false
console.log(Number.isInteger(-1)); // 👉️ true

On each iteration, we check if the current element is an integer and return the result.

The new array contains only the integer values of the original array.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Filter an Array with Multiple Conditions in JavaScript
• Filter an Array of Objects based on a property - JavaScript