// 提取固定字符之间的字符串
function getInnerString(source, prefix, postfix) {
 var regexp = new RegExp(encodeReg(prefix) + '.+' + encodeReg(postfix), 'gi');
 var matches = String(source).match(regexp);
 var formatedMatches = _.map(matches, value => {
  return value
   .replace(prefix, '')
   .replace(postfix, '');
 });
 return formatedMatches;
}

//转义影响正则的字符
function encodeReg(source) {
 return String(source).replace(/([.*+?^=!:${}()|[\]/\\])/g,'\\$1');
}

var a = '让我们荡起双桨吧';
getInnerString(a, '让我们', '吧'); // ['双桨']

var b = '老总和不在办公室，有事请留言给李秘书';
getInnerString(b, '有事请留言给', ''); // ['李秘书']