JavaScript RegExp [0-9] Expression

The [0-9] expression in JavaScript regular expressions matches any single digit between 0 and 9. It is a character class used to represent a range of numeric characters.

let regex = /[0-9]/g;
let str = "abc123xyz";
let matches = str.match(regex);
console.log(matches);

[ '1', '2', '3' ]

The pattern [0-9] matches the digits 1, 2, and 3 in the string.

Syntax:

/[0-9]/  

• [0-9]: Matches a single numeric character (0 through 9).
• Modifiers (optional): Can be used with flags like g, i, or m for global, case-insensitive, or multiline matching.

Key Points

• Matches any digit from 0 to 9.
• Equivalent to the shorthand \d in JavaScript regex.
• Used in conjunction with quantifiers to match multiple digits or numeric patterns.
• Works within larger patterns for specific use cases, such as parsing numbers from strings.

Real-World Examples

1. Finding Digits in a String

let regex = /[0-9]/g;
let str = "Contact: 555-123-4567";
let matches = str.match(regex);
console.log(matches);

[
  '5', '5', '5', '1',
  '2', '3', '4', '5',
  '6', '7'
]

2. Extracting Numbers

let regex = /[0-9]+/g;
// Matches one or more digits
let str = "The order IDs are 123, 456, and 789.";
let matches = str.match(regex);
console.log(matches);

[ '123', '456', '789' ]

The + quantifier ensures that consecutive digits are matched as a single number.

3. Validating Numeric Input

let regex = /^[0-9]+$/;
let input = "123456";
if (regex.test(input)) {
    console.log("Valid numeric input.");
} else {
    console.log("Invalid input.");
}

Valid numeric input.

The pattern ^[0-9]+$ ensures the entire string consists only of digits.

4. Matching Numbers in a Date

let regex = /[0-9]{4}/;
// Matches exactly four digits
let str = "The year is 2024.";
let match = str.match(regex);
console.log(match);

[ '2024', index: 12, input: 'The year is 2024.', groups: undefined ]

Here, [0-9]{4} matches a four-digit sequence representing a year.

5. Replacing Digits

let regex = /[0-9]/g;
let str = "Room 101";
let result = str.replace(regex, "*");
console.log(result);

Room ***

This example replaces all digits in the string with asterisks (*).

Common Patterns Using [0-9]

• Match a Single Digit:

/[0-9]/

• Match Multiple Digits:

/[0-9]+/

• Match a Fixed Number of Digits:

/[0-9]{3}/ // Matches exactly 3 digits

• Match Digits at the Start of a String:

/^[0-9]+/

• Match Digits Within Non-Digit Characters:

/\b[0-9]+\b/

Comparison: [0-9] vs \d

• [0-9]: Matches only numeric characters (0 to 9).
• \d: Matches numeric characters, but may match additional Unicode digits depending on the environment.

For strict numeric matching, [0-9] is often preferred.

Why Use [0-9]?

• Precision: Clearly specifies a range of numeric characters.
• Versatility: Works seamlessly with other regex patterns and modifiers.
• Control: Provides explicit control over matching rules, avoiding ambiguity.

Conclusion

The [0-9] expression is a fundamental building block in JavaScript regex, perfect for handling numeric data in strings.

Recommended Links:

• JavaScript RegExp Complete Reference
• JavaScript Cheat Sheet-A Basic guide to JavaScript
• JavaScript Tutorial