Regular expression for numbers and one decimal

Question

I can't seem to get a simple regular expression to work. Here's what I have at the moment:

$(".Hours").on('input', function (e) {

    var regex = /^\d+(\.\d{0,2})?$/g;

    if (!regex.test(this.value)) {
        if (!regex.test(this.value[0]))
            this.value = this.value.substring(1, this.value.length);
        else
            this.value = this.value.substring(0, this.value.length - 1);
    }
});

I need the user to be able to only enter numbers and one decimal (with only two numbers after the decimal). It's working properly now, with the exception that a user cannot start with a decimal.

Acceptable:

23.53
0.43
1111.43
54335.34
235.23
.53 <--- Not working 

Unacceptable:

0234.32 <--- The user can currently do this
23.453
1.343
.234.23
1.453.23

Any help on this?

Solution 1

Updated answer:

RegExp -

^(?:0|[1-9]\d+|)?(?:.?\d{0,2})?$

Explanation at regex101:

Original answer:

fiddle Demo

RegExp -

^(\d+)?([.]?\d{0,2})?$

Explanation

Assert position at the beginning of the string «^»
Match the regular expression below and capture its match into backreference number 1 «(\d+)?»
   Between zero and one times, as many times as possible, giving back as needed (greedy) «?»
   Match a single digit 0..9 «\d+»
      Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
Match the regular expression below and capture its match into backreference number 2 «([.]?\d{0,2})?»
   Between zero and one times, as many times as possible, giving back as needed (greedy) «?»
   Match the character “.” «[.]?»
      Between zero and one times, as many times as possible, giving back as needed (greedy) «?»
   Match a single digit 0..9 «\d{0,2}»
      Between zero and 2 times, as many times as possible, giving back as needed (greedy) «{0,2}»
Assert position at the end of the string (or before the line break at the end of the string, if any) «$»

Solution 2

Would this meet your needs:

var regex = /^\d+([.]?\d{0,2})?$/g;

Solution 3

Your regex: var regex = /^\d+(\.\d{0,2})?$/g;

What you need: var regex = /^\d*(\.\d{1,2})?$/;

You were requiring at least one digit before the decimal (\d+). I have also changed it so if you include a decimal, there must be at least one digit after it.

Comments

[Blazemonger]

Why are you testing this.value and this.value[0]?

[Dylan Vester]

There is a minor bug in your regular expression. The decimal point wasn't escaped, so it was being processed as any single character. So it was allowing the number to start with basically anything (e.g. a24, b24, b50). Correct Regex ^(?:0|[1-9]\d+|)?(?:\.?\d{0,2})?$

[Barry]

The regex doesn't work. 2.2, for example is not matched. Any single digit followed by '.' won't match. Your regex requires two digits before '.'.