do you know how to modify the regex to allow one ‘-‘ char at the beginning of the string

i have the existing regex pattern: /^-?(?!0d)d+.?d*$/,

Currently the above regex do not allow – char at beginning of the string

Do you know how to modify the regex to also allow one ‘-‘ input besides the above existing validation My attempt:

/^(?!0d)d+.?d*$/

but it doesn’t work well.

Answer

To modify the regex and accept only a - as well, you could make 2 optional parts, and assert that the string is not empty.

^(?!-?0d|$)-?(?:d+.?d*)?$

• ^ Start of string
• (?!-?0d|$) Assert not optional - 0 and digit or end of string
• -? Match optional -
• (?:d+.?d*)? Optionally match 1+ digits, optional . and 0+ digits
• $ End of string

Regex demo