How do you write a JS regular expression to extract the first "2" from "/?page=2&promo_id=1234". (ie page number 2)
Thanks!
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2Start here. developer.mozilla.org/en/JavaScript/Guide/Regular_ExpressionsMatt Ball– Matt Ball2011-05-16 22:25:30 +00:00Commented May 16, 2011 at 22:25
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4 Answers
This should do the trick.
var match = /page=(\d+)/.exec("/?page=2&promo_id=1234"), pageNum = match[1];
2 Comments
Thomas Hupkens
I wrote a solution very close to yours, but they had both the same issue: if it doesn't match (say, because there is no number), JS will try to read the 2nd element of a null-value, and crash…
Z. Zlatev
that's quite context specific but
|| undefined at the end should work it out.var extractPageNumber = function(s) {
var r=/page=(\d+)/, m=(""+s).match(r);
return (m) ? Number(m[1]) : undefined;
};
extractPageNumber("/?page=2&promo_id=1234"); // => 2
extractPageNumber("/?page=321&promo_id=1234"); // => 321
extractPageNumber("foobar"); // => undefined
Comments
It depend on what may vary in your string. If the number is the only variable, then:
var match, pageNumber;
if(pageNumber = "/?page=2&promo_id=1234".match(/page=(\d+)/))
pageNumber = match[1];
Or the ugly (but shorter) way
var pageNumber = ("/?page=223&promo_id=a".match(/page=(\d+)/)||[,undefined])[1]
Comments
I wouldn't use regular expressions as such, I'd use the split method:
var str="/?page=2&promo_id=1234";
document.write(str.split("/?page=")[1][0]);
Of course this will only work for single digit numbers. You could modify it to work for all numbers using a proper regular expression.
