Looking for a regex to parse parameters string for JS

Question

I cannot find out the regex to get param value from the part of query string:

I need to send parameter name to a method and get parameter value as result for string like "p=1&qp=10". I came up with the following:

function getParamValue(name) {

  var regex_str = "[&]" + name + "=([^&]*)";

  var regex = new RegExp(regex_str);

  var results = regex.exec(my_query_string);
  // check if result found and return results[1]

}

My regex_str now doesn't work if name = 'p'. if I change regex_str to

var regex_str = name + "=([^&]*)";

it can return value of param 'qp' for param name = 'p'

Can you help me with regex to search the beginning of param name from right after '&' OR from the beginning of a string?

possible duplicate of Use the get parameter of the url in javascript and many other questions. — Felix Kling
– Felix Kling, Commented May 10, 2012 at 15:28

score 1 · Accepted Answer · 2012-05-10 16:18:56Z

1

This might work, depending on if you have separated the parameter part.

var regex_str = "(?:^|\&)" + name + "=([^&]*)";
or
var regex_str = "(?:\&|\?)" + name + "=([^&]*)";

edited May 10, 2012 at 16:18

answered May 10, 2012 at 16:06

user557597

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Alexander Pavlov · Accepted Answer · 2012-05-10 15:43:30Z

1

Looks like split will work better here:

var paramsMap = {};
var params = string.split("&");
for (var i = 0; i < params.length; ++i) {
    var keyValue = params[i].split("=", 2);
    paramsMap[keyValue[0]] = keyValue[1];
}

If you desperately want to use a regex, you need to use the g flag and the exec method. Something along the lines of

var regex = /([^=]+)=([^&]+)&?/g;
var paramsMap = {};
while (true) {
    var match = regex.exec(input);
    if (!match)
        break;
    paramsMap[match[1]] = match[2];
}

Please note that since the regex object becomes stateful, you either need to reset its lastIndex property before running another extraction loop or use a new RegExp instance.

edited May 10, 2012 at 15:43

answered May 10, 2012 at 15:28

Alexander Pavlov

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1 Comment

make_sense Over a year ago

I agree but I am also interested in the solution for educational reason :)

Osmaan Shah · Accepted Answer · 2012-05-10 19:05:47Z

1

Change your regex string to the following:

//pass the query string and the name of the parameter's value you want to retrieve
function getParamValue(my_query_string , name)
{
    var regex_str = "(?:^|\&)" + name + "\=([^&]*)";
    var regex = new RegExp(regex_str);
    var results = regex.exec(my_query_string); 
    try
    {
        if(results[1] != '')
        {
            return results[1];
        }
    }
    catch(err){};
    return false;
}

edited May 10, 2012 at 19:05

answered May 10, 2012 at 15:47

Osmaan Shah

3552 silver badges8 bronze badges

1 Comment

user557597 Over a year ago

[\?\&]? will be ignored, allowing name to be preceeded with anything. \=(((?!\&).)*) is equivalent to and more efficient as ([^&]*)

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