I have this string

/results?radius=4000&newFilter=true

and I need to replace radius=4000 with radius=n where n is a variable.

How can I use String.replace() method with regex to match that part?

I have this string

/results?radius=4000&newFilter=true

and I need to replace radius=4000 with radius=n where n is a variable.

How can I use String.replace() method with regex to match that part?

• javascript
• regex

• It would be better to create an object literal of your params, then simply replace the value and redirect with new params. – Tim Vermaelen Commented Apr 7, 2017 at 15:13
• Here and here. – revo Commented Apr 7, 2017 at 15:14
• 2 Possible duplicate of How can I replace a regex substring match in Javascript? – revo Commented Apr 7, 2017 at 15:15

6 Answers 6

You can use /radius=\d+/ to match "radius=" followed by any number of digits. With this we can use the replace() method to replace it with the desired value:

var str = "/results?radius=4000&newFilter=true";
var replacement = 123;

var newStr = str.replace(/radius=\d+/, "radius=" + replacement);

console.log(newStr);

If you want to get all parameters you can try this :

function getParams(uri) {

	var params = {},
        tokens,
        re = /[?&]?([^=]+)=([^&]*)/g;
        
    while (tokens = re.exec(uri)) {
        params[decodeURIComponent(tokens[1])] = decodeURIComponent(tokens[2]);
    }
    return params;
}

var str='/results?radius=4000&newFilter=true';

str = str.substring(str.indexOf("?"));
params = getParams(str);

console.log(params);
console.log('radius => ', params['radius']);

This answer is from this post: How to get the value from the GET parameters?

It should be as easy as

var str='/results?radius=4000&newFilter=true';
var n = 1234;

str = str.replace(/(radius=)(\d+)/, "$1" + n);

var url = "/results?radius=4000&newFilter=true"; 
// or window.location.href for current url
var captured = /radius=([^&]+)/.exec(url)[1]; // your 4000
var newValue = 5000;
url = url.replace(captured, newValue);

by this way you can use it to get all your requested parameters too and it is not decimal binded

ES6 with regex using positive lookbehind

const string       = '/results?radius=4000&newFilter=true',
      n            = '1234',
      changeRadius = (radius) => string.replace(/(?<=radius=)\d+/, n);

console.log(changeRadius(n));

/* Output console formatting */
.as-console-wrapper { top: 0; }

• changeRadius is function that takes one parameter (radius) and performs replacement.
• About the regex: \d+ gets as many digits as possible, (?<=STRING) is a positive lookbehind.

Other regex

Body of changeRadius() function can be replaced with string.replace(/radius=\d+/, 'radius=' + n). It probably has better performance, but original regex is more direct translation of the problem.

You can use capturing without remembering the match to capture only the numerical value after 'radius='.

var url = "/results?radius=4000&newFilter=true";

var radius = 123;

var newUrl = url.replace(/(?:radius=){1}(\d+)/, radius);

console.log(newUrl); // logs '/results?radius=4000&newFilter=true'0

'