Regular expression in javascript

Question

here is the code

var str = 'a girl is reading a book!';
var reg =  /\w*(?=ing\b)/g;
var res = str.match(reg);
console.log(res);

result is ["read",""] in chrome.

I wanna ask why there is "" in the result.

Answer 1

This is expected behaviour

First read is captured since it is followed by ing.Here ing is only matched..It is never included in the result.

Now we are at the position after read i.e we would be at i..here again ing matches(due to \w*) and it gives an empty result because there is nothing between read and ing.

You can use \w+(?=ing\b) to avoid the empty result

Answer 2

/\w*(?=ing\b)/g
Here you are using * which means none or more, Hence it captures both "read"ing and ""ing after it reads the read part. Use + for one or more.