将$ _GET变量赋给JS变量

www.mywebsite.com/?foo=bar

How can I get the value of foo into a Javascript variable?

You don't even need PHP for that. Basically, you can parse window.location.href to get the value of a GET URL parameter into a JavaScript variable.

There is plenty of code online, you can use for example this:

function getUrlParameter( name )
{
  name = name.replace(/[\[]/,"\\\[").replace(/[\]]/,"\\\]");
  var regexS = "[\\?&]"+name+"=([^&#]*)";
  var regex = new RegExp( regexS );
  var results = regex.exec( window.location.href );
  if( results == null )
    return "";
  else
    return results[1];
}

To get the value of foo, just call getUrlParameter("foo") in your JavaScript code.

You can parse the window.location.search string for query variables.

https://developer.mozilla.org/en/DOM/window.location

For example

var query = window.location.search.substring(1);
var pairs = query.split('&');
var _get = {};
for (var i = 0; i < pairs.length; i++) {
    var pair = pairs[i].split('=');
    _get[pair[0]] = pair[1];
}

I did some googling and here is a link for you http://www.zrinity.com/developers/code_samples/code.cfm/CodeID/59/JavaScript/Get_Query_String_variables_in_JavaScript

You can try this

 function getUrlVars()
{
var vars = [], hash;
var hashes = window.location.href.slice(window.location.href.indexOf('?') + 1).split('&');
for(var i = 0; i < hashes.length; i++)
{
    hash = hashes[i].split('=');
    vars.push(hash[0]);
    vars[hash[0]] = hash[1];
}
return vars;
}

EDIT

The above will parse the URL and give you the parameters as an associative array. You can also try

function getURLVars(name) {
return decodeURI(
    (RegExp(name + '=' + '(.+?)(&|$)').exec(location.search)||[,null])[1]
 );
}

In this if you want the value of foo, call this with getUrlVars('foo')