正则表达式2

• $1, $2, ...
• api参数或返回值
  var url = "http://blog.163.com/album?id=1#comment";
  var reg = /(https?:)//([^/]+)(/[?])?(?[^#])?(#.*)?/;
  var arr = url.match(reg);
  var protocol = arr[1];
  var host = arr[2];
  var pathname = arr[3];
  var search = arr[4];
  var hash = arr[5];

替换一个子串
var str = "The price of tomato is 5.";
str.replace(/(\d+)/, "$1.00"); // => The price of tomato is 5.00.

var str = "The price of tomato is 5, the price of apple is 10."
str.replace(/(\d+)/g, "$1.00");  // => The price of tomato is 5.00, the price of apple is 10.00.

var html = "<label>网址：</label><input placeholder="以http://起始">";
html = html.replace(/[<>]/g, function (m0) {
  switch(m0) {
    case "<":
      return "&lt;";
    case ">":
      return "&gt;";
  }
});