Get the First Number in a String using JavaScript

Get the First Number in a String #

To get the first number in a string:

1. Use the search() method to get the index of the first number in the string.
2. The search method takes a regular expression and returns the index of the first match in the string.
3. Access the string at the index, using bracket notation.

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const str = 'one 2 three 4';

const index = str.search(/[0-9]/);
console.log(index); // 👉️ 4

const firstNum = Number(str[index]);
console.log(firstNum); // 👉️ 2

We used the String.search method to get the index of the first digit in the string.

The only parameter the method takes is a regular expression.

The forward slashes / / mark the beginning and end of the regular expression.

The part between the square brackets [] is called a character class and matches a range of digits from 0 to 9.

The next step is to access the string at the specific index using bracket notation and convert the string to a number.

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console.log('test'.search(/[0-9]/)); // 👉️ -1

If you then try to access the string at index -1, you would get undefined back.

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console.log('test'[-1]); // 👉️ undefined

If you have to handle this scenario, you can use an if statement.

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const str = 'one 2 three 4';

const index = str.search(/[0-9]/);

if (index !== -1) {
  console.log('✅ String contains at least 1 number');
  const firstNum = Number(str[index]);
  // firstNum is defined only here
} else {
  console.log('⛔️ String does not contain any numbers');
}

In this example, we only declare the firstNum variable if the search method matched at least 1 digit in the string.

Further Reading #

• Get the Number from the End of a String in JavaScript
• Get the Index of the First Number in a String in JavaScript