JavaScript regular expression for decimal numbers

Question

I'm looking for a regular expression in JavaScript that tests whether a string is a number with one or two digits before the decimal point and optionally a maximum of five digits after decimal point.

Examples of correct values:

• 12.345
• 12.12
• 1.3
• 1.12345
• 12

What would be the correct regex for this?

Answer 1

Regex

/^\d{1,2}(\.\d{1,5})?$/

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Demo

var regexp = /^\d{1,2}(\.\d{1,5})?$/;

console.log("'10.5' returns " + regexp.test('10.5'));
console.log("'100.5' returns " + regexp.test('100.5'));
console.log("'82.744' returns " + regexp.test('82.744'));
console.log("'13.' returns " + regexp.test('13.'));
console.log("'.744' returns " + regexp.test('.744'));
console.log("'.74400' returns " + regexp.test('.74400'));
console.log("'5.74400' returns " + regexp.test('5.74400'));

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Explanation

1. / / : the beginning and end of the expression
2. ^ : whatever follows should be at the beginning of the string you're testing
3. \d{1,2} : there should be one or two digits here
4. ( )? : this part is optional
5. \. : here goes a dot
6. \d{1,5} : there should be between one and five digits here
7. $ : whatever precedes this should be at the end of the string you're testing

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Tip

You can use regexr.com or regex101.com for testing regular expressions directly in the browser!

Answer 2

you can try that:

^\d{1,2}(\.\d{1,5})?$

Explanation:

1. ^ start of a string
2. \d{1,2} 1 to 2 digit number
3. ( opening capture group
4. \. dot
5. \d{1,5} number 1 to 5 digit
6. ) closing capture group
7. ? makes the entire capture group optional

$ end of string

Demo

const regex = /^\d{1,2}(\.\d{1,5})?$/gm;
const str = `12.121`;

console.log(regex.test(`12.121`));
console.log(regex.test(`1`));
console.log(regex.test(`1.1`));
console.log(regex.test(`12.123`));
console.log(regex.test(`1.123`));
console.log(regex.test(`1.1234567`));