Regex returns string undefined

问题

I am trying to extract hash value from an magnet link but it returns undefined

var tesst = "magnet:?xt=urn:btih:2B78EDFDDC87DC9605FB285997A80B787888C194&"
var test = tesst.match(/magnet:\?xt=urn:btih:[a-z\d]{40}\&/im);
alert (test[1]);

I cant understand what I am doing wrong.

回答1:

just mark what you want with capturing group:

/^magnet:\?xt=urn:btih:([a-z\d]{40})\&$/im

Also I recomend to not use regexp here.
Try followed:

tesst.split(':')[3].slice(0, -1);

slice(0, -1) used for remove last '&', you can use any other method, like slice(0, 40), replace(/[^\w]/g, '') or any other.

回答2:

var test = tesst.match(/magnet:\?xt=urn:btih:([a-z\d]{40})\&/im);

You forgot the ( ) around the hash part.

回答3:

You need to include [a-z\d]{40} part inside a capturing group and you don't need to escape & symbol, because it isn't a regex meta character.

> var test = tesst.match(/magnet:\?xt=urn:btih:([a-z\d]{40})&/im);
undefined
> console.log(test[1])
2B78EDFDDC87DC9605FB285997A80B787888C194

回答4:

You can use this regex

/([^:]+)&$/

and use test[1]

console.log(str.match(/([^:]+)&$/)[1]);

来源：https://stackoverflow.com/questions/27380962/regex-returns-string-undefined