get url parameter by name with javascript

getParameterByName.js

var getParameterByName = function (field, url) {
	 var href = url ? url : window.location.search;
	 // replace '[' and ']' character for '\[' and '\]'
    field = field.replace(/[\[]/, "\\[").replace(/[\]]/, "\\]");
    var regex = new RegExp("[\\?&]" + field + "=([^&#]*)"),
    results = regex.exec(href);
    return results === null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}

This function is from stackoverflow.I think it has some problems.It can't handle these urls.

1. http://example.com/t?a[1[231]=bbb
2. multiple values
   http://example.com/t?field1=value1&field1=value2&field2=value3
3. query string's key has reserved words
   http://example.com/t?a+b=bbb

var getParameterByName = function (field, url) {
     var href = url ? url : window.location.search;
    field = field.replace(/[\[]/g, "\\[").replace(/[\]]/g, "\\]");
    var regex = new RegExp("[\\?&]" + field + "=([^&#]*)"),
    results = regex.exec(href);
    return results === null ? "" : decodeURIComponent(results[1].replace(/\+/g, " "));
}