en.javascript.info/10-regular-expressions-javascript/09-regexp-groups/3-find-decimal-positive-numbers/solution.md

An integer number is pattern:\d+.

A decimal part is: pattern:\.\d+.

Because the decimal part is optional, let's put it in parentheses with quantifier pattern:'?'.

Finally we have the regexp: pattern:\d+(\.\d+)?:

let reg = /\d+(\.\d+)?/g;

let str = "1.5 0 12. 123.4.";

alert( str.match(re) );   // 1.5, 0, 12, 123.4