Extract a Number from a String using JavaScript

We will extract the numbers if they exist in a given string. We will have a string and we need to print the numbers that are present in the given string in the console.

Below are the methods to extract a number from string using JavaScript:

JavaScript match method with regEx to extract a number from a string

The number from a string in JavaScript can be extracted into an array of numbers by using the match method. This function takes a regular expression as an argument and extracts the number from the string. The regular expression for extracting a number is (/(\d+)/). 

Example 1: This example uses the match() function to extract numbers from strings with regular expressions. 

// Function to extract numbers
function myGeeks() {

    // Input string
    let str = "jhkj7682834";
    console.log(str)

    // Using match with regEx
    let matches = str.match(/(\d+)/);
    
    // Display output if number extracted
    if (matches) {
        console.log(matches[0]);
    }
}

// Function call
myGeeks();

jhkj7682834
7682834

Example 2: This example uses the match() function to extract numbers from strings. 

// Function to extract numbers
function myGeeks() {

    // Input string
    let str = "foo35bar5jhkj88";
    console.log(str)

    // Using match with regEx
    let matches = str.match(/\d+/g);
    
    // Display output if number extracted
    if (matches) {
        console.log(matches[0] +', '+ matches[1]+', ' + matches[2]);
    }
}

// Function call
myGeeks();

foo35bar5jhkj88
35, 5, 88

JavaScript reduce() method with the spread operator to extract a number from a string

The Javascript arr.reduce() method in JavaScript is used to reduce the array to a single value and executes a provided function for each value of the array (from left to right) and the return value of the function is stored in an accumulator. 

Example: This example spread operator to convert into an array and the reduce method to extract all the numbers from the string.

// Function to extract numbers
function myGeeks() {
    // Input string
    let str = "jhkj7682834";
    let c = "0123456789";
    console.log(str);
    function check(x) {
        return c.includes(x) ? true : false;
    }
    let matches = [...str].reduce(
        (x, y) => (check(y) ? x + y : x),"");

    // Display output if number extracted
    if (matches) {
        console.log(matches);
    }
}

// Function call
myGeeks();

jhkj7682834
7682834

JavaScript replace() method with regEx to extract a number from a string

The string.replace() is an inbuilt method in JavaScript that is used to replace a part of the given string with another string or a regular expression. The original string will remain unchanged.

Example: In this example, we will use the JavaScript replace() method with regEx to extract the numbers out of given string

// Function to extract numbers
function myGeeks() {
    // Input string
    let str = "jhkj7682834";
    console.log(str);

    // Using match with regEx
    let matches = str.replace(/[^0-9]/g, "");

    // Display output if number extracted
    if (matches) {
        console.log(matches);
    }
}

// Function call
myGeeks();

jhkj7682834
7682834

JavaScript for loop to extract a number from a string

This approach loops through each character in the string and checks if it's a number using isNaN(). If the character is a number, it appends it to numberStr.

Example: This example use for loop to extract all numbers present in the string.

function extractNumbers(str) {
    let numbers = "";
    for (let i = 0; i < str.length; i++) {
        if (!isNaN(str[i])) {
            numbers += str[i];
        }
    }
    console.log(numbers)
}

// Input string
let str = "jhkj7682834hhdg237";
console.log(str);
extractNumbers(str);

jhkj7682834hhdg237
7682834237

Using Array..filter with split

Using Array..filter with split, you can extract numbers from a string by splitting the string into an array of characters, filtering out non-numeric characters, and joining the remaining characters back into a string.

Example:

let str = "The price is 123 dollars";
let number = str.split('').filter(char => !isNaN(char) && char !== ' ').join('');
console.log(number); // "123"

123

JavaScript is best known for web page development but it is also used in a variety of non-browser environments. You can learn JavaScript from the ground up by following this JavaScript Tutorial and JavaScript Examples.