What is the simplest and most correct way to validate a decimal number in Javascript?
For example, how to implement a IsNumeric function that has the following Test Cases:
IsNumeric('-1') true
IsNumeric('-1.5') true
IsNumeric('0') true
IsNumeric('0.42') true
IsNumeric('.42') true
IsNumeric('99,999') false
IsNumeric('0x89f') false
IsNumeric('#abcdef')false
IsNumeric('1.2.3') false
IsNumeric('') false
IsNumeric('blah') false
I believe it would be through the use of a regular expression. An expression that satisfies all your proposed tests would be:
^-?\d*\.?\d+$
Example in jsFiddle . Explaining:
^ start of string -? with or without forward \d* zero or more digits (so that .42 validates, it is important to accept zero digits before the point) \.? with or without dot \d+ one or more digits $ end of string Other expressions could be used if you wanted to accept a larger range of numbers - such as grouping thousands using the comma (American standard), permitting scientific notation using e (common in programming languages), allowing% in front of only one less, etc. And an "obvious" problem with the proposed expression is that it does not reject numbers with leading zeros.
In the end, it's a matter of accurately identifying what format a string might be expected to have to be considered "numeric" and adjusting the expression accordingly. It may become a bit large, but in my opinion this is still simpler than trying a parse manual (only if what you consider "number" does not fit into a regular language is that a more sophisticated method becomes necessary.)