Is there function which work as:
var regex=/\s*(\w+)/;
var s="abc def ";
var m1=regex.exec(s,0); // -> matches "abc"
var m2=regex.exec(s,3); // -> matches "def"
I know the alternative is:
var regex=/\s*(\w+)/;
var s="abc def ";
var m1=regex.exec(s); // -> matches "abc"
var m2=regex.exec(s.substring(3)); // -> matches " def"
But I worry about that if s is very long and s.substring is called many times, some implementation may work in bad efficiency in which copy long strings many times.
Yes, you can make exec start at a particular index if the regex has the g global modifier.
var regex=/\s*(\w+)/g; // give it the "g" modifier
regex.lastIndex = 3; // set the .lastIndex property to the starting index
var s="abc def ";
var m2=regex.exec(s); // -> matches "def"
If your first code example had the g modifier, then it would work as you wrote it, for the very same reason above. With g, it automatically sets the .lastIndex to the index past the end of the last match, so the next call would start there.
So it depends on what you need.
If you don't know how many matches there will be, the common approach would be to run exec in a loop.
var match,
regex = /\s*(\w+)/g,
s = "abc def ";
while(match = regex.exec(s)) {
alert(match);
}
Or as a do-while.
var match,
regex = /\s*(\w+)/g,
s = "abc def ";
do {
match = regex.exec(s);
if (match)
alert(match);
} while(match);
g, which is probably the way the OP wants to do things. :)
.lastIndex if you ultimately want all the matches in the string. You'd just do like your first example, but include g. Or you can run exec in a loop. I'll update with a loop example.
a_string_with_words_separated_with_space.split(/\s+/);I don't think there is any regular expression method that can do this. If you are worried about performance, I would just store the full string and the snipped string so substring is only ever called once:
var regex=/\s*(\w+)/;
var s="abc def ";
var shorts = s.substring(3);
var m1=regex.exec(s); // -> matches "abc"
var m2=regex.exec(shorts); // -> matches " def"
.{3}at the beginning of the regex.\w+and then walk each individual match? I'm guessing this is a reduction of your actual scenario, though...substringmakes a new object, but does not necessarily copy the character data. The length of your string may well be irrelevant. At any rate, to ensure you don't have an X-Y problem here, consider using thegflag, since you are probably trying to find words over and over again, right?