正则表达式：匹配倒数第二个字符

Question

I need to wrap the two last characters in a string in a separate <span> :

-1:23 // This is what I have
-1:<span>2</span><span>3</span> // This is what I want

The following matches the last character – but how can I make it match the second last as well?

str.replace(/(.$)/, "<span>$1</span>");

Thanks :)

Answer 1

You may use

.replace(/.(?=.?$)/g, "<span>$&</span>")

See the regex demo

If these must be digits, replace . with \\d :

.replace(/\d(?=\d?$)/g, "<span>$&</span>")

The pattern matches

• \\d - a digit
• (?=\\d?$) - that is followed with an end of string or a digit and end of string.

The $& is a replacement backreference that references the whole match value from the string replacement pattern.

JS demo:

 console.log("-1:23".replace(/.(?=.?$)/g, "<span>$&</span>")); console.log("-1:23".replace(/\\d(?=\\d?$)/g, "<span>$&</span>")); 

Now, to make it more dynamic, you may use a limiting (range/interval) quantifier :

 function wrap_chars(text, num_chars) { var reg = new RegExp(".(?=.{0," + (num_chars-1) + "}$)", "g"); return text.replace(reg, "<span>$&</span>"); } console.log(wrap_chars("-1:23", 1)); // wrap one char at the end with span console.log(wrap_chars("-1:23", 2)); // wrap two chars at the end with span 

Answer 2

You can add another group before the last one, which also matches a single character ( (.) ), then wrap each of them using references ( $1 and $2 ):

 var str = '-1:23'.replace(/(.)(.)$/, '<span>$1</span><span>$2</span>') console.log(str);