Per comment of OP/modified question, if you want 1 or 2 digits, optionally followed by (a period, followed by 1 or 2 more digits), you could use this regex:
var regex = /^\d{1,2}(\.\d{1,2})?$/;
// The ( ) groups several things together sequentially.
// The ? makes it optional.
If you want 1 or 2 digits, followed by a period, followed by 1 or 2 more digits:
var regex = /^\d{1,2}\.\d{1,2}$/;
// The / denotes the start and end of the regex.
// The ^ denotes the start of the string.
// The $ denotes the end of the string.
// The \d denotes the class of digit characters.
// The {1,2} denotes to match 1 to 2 occurrences of what was encountered immediately to the left.
// The \. denotes to match an actual . character; normally . by itself is a wildcard.
// happy paths
regex.test('00.00'); // true
regex.test('0.00'); // true
regex.test('00.0'); // true
regex.test('0.0'); // true
regex.test('12.34'); // true (test other digits than '0')
// first half malformed
regex.test('a0.00'); // non-digit in first half
regex.test('.00'); // missing first digit
regex.test('000.00'); // too many digits in first half
// period malformed
regex.test('0000'); // missing period
regex.test('00..00'); // extra period
// second half malformed
regex.test('00.a0'); // non-digit in second half
regex.test('00.'); // missing last digit
regex.test('00.000'); // too many digits in second half
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solved How to create Regex for 00.00?