angularregexangular-formbuilderangular-custom-validators

Regex prevents values ​less than or equal to zero and accepts decimal values


Hello I'm building a form in Angular with FormBuilder and i want to put a validation in Validators.pattern() that prevents values ​​less than or equal to zero and that accepts decimal values

How would the regex expression look? Thanks.


Solution

  • Don't. Sure, you could use something like ^([1-9]\d*(\.\d+)?|0\.\d+)$, but you're better off restricting the input in other ways, like <input type="number" id="quantity" name="quantity" min="0"> for example.


    Explanation of the regex

    First of all, it's anchored between ^ and $, so the entire input must be matched. Then, there are two options, separated by |:

    1. [1-9] a digit between 1 and 9
      \d* followed by any number of digits
      (\.\d+)? optionally followed by a decimal point and at least one digit

    2. 0 a zero
      \.\d+ followed by a decimal point and at least one digit

    Note that if it starts with a zero, the decimal point and a following digit are mandatory, while if there's any other leading digit, the decimal point and following digits are optional, although if there is a decimal point, there should be at least one digit after that.