问通过JavaScript提取字符串的特定部分

EN

> var s = 'http://you.tumblr.com/api/read/json';
> var re = /^http:\/\/(\w+)\./;
> s.match(re);
[ 'http://you.',
  'you',
  index: 0,
  input: 'http://you.tumblr.com/api/read/json' ]
> s.match(re)[1]
'you'

'http://you.tumblr.com/api/read/json'.match(/^http:\/\/(\w+)\./)[1]

'you'

^            match start of string
http:\/\/    match http://
(\w+)        match group of word characters which appears 1 or more times
\.           match a dot

var str = "http://mydomain.tumblr.com/api/read/json";
var domainpart = str.substr(7, str.indexOf(".") - 7);
document.write(domainpart);