How to create query parameters in Javascript?

Is there any way to create the query parameters for doing a GET request in JavaScript?

Just like in Python you have urllib.urlencode(), which takes in a dictionary (or list of two tuples) and creates a string like 'var1=value1&var2=value2'.

Here you go:

function encodeQueryData(data) {
   const ret = [];
   for (let d in data)
     ret.push(encodeURIComponent(d) + '=' + encodeURIComponent(data[d]));
   return ret.join('&');
}

Usage:

const data = { 'first name': 'George', 'last name': 'Jetson', 'age': 110 };
const querystring = encodeQueryData(data);

URLSearchParams has increasing browser support.

const data = {
  var1: 'value1',
  var2: 'value2'
};

const searchParams = new URLSearchParams(data);

// searchParams.toString() === 'var1=value1&var2=value2'

Node.js offers the querystring module.

const querystring = require('querystring');

const data = {
  var1: 'value1',
  var2: 'value2'
};

const searchParams = querystring.stringify(data);

// searchParams === 'var1=value1&var2=value2'

functional

function encodeData(data) {
    return Object.keys(data).map(function(key) {
        return [key, data[key]].map(encodeURIComponent).join("=");
    }).join("&");
}   

Zabba has provided in a comment on the currently accepted answer a suggestion that to me is the best solution: use jQuery.param().

If I use jQuery.param() on the data in the original question, then the code is simply:

const params = jQuery.param({
    var1: 'value',
    var2: 'value'
});

The variable params will be

"var1=value&var2=value"

For more complicated examples, inputs and outputs, see the jQuery.param() documentation.