Proper way to parse Boolean query string param in node/express

Docs if you are using query-string

const queryString = require('query-string');

queryString.parse('foo=true', {parseBooleans: true});
//=> {foo: true}

The only thing I would change about your approach is to make it case insensitive:

var isUpdated = ((req.query.isUpdated+'').toLowerCase() === 'true')

You could make this a utility function as well if you like:

function queryParamToBool(value) {
  return ((value+'').toLowerCase() === 'true')
}
var isUpdated = queryParamToBool(req.query.isUpdated)

I use this pair of lines:

let test = (value).toString().trim().toLowerCase(); let result = !((test === 'false') || (test === '0') || (test === ''));

Here is my generic solution for getting a query params as a boolean:

const isTrue = Boolean((req.query.myParam || "").replace(/\s*(false|null|undefined|0)\s*/i, ""))

It converts the query param into a string which is then cleaned by suppressing any falsy string. Any resulting non-empty string will be true.

var myBoolean = (req.query.myParam === undefined || req.query.myParam.toLowerCase() === 'false' ? false : true)

My one-liner snippet:

const isTruthy = (val) => val && !['false', '0', ''].includes(val.toString().trim().toLowerCase());

Use JSON.parse for checking the boolean value in query params like this:

var isUpdated = JSON.parse(req.query.isUpdated)?true: false;

You can use qs package

A little code to parse int and booleans

qs.parse(request.querystring, {
      decoder(str, decoder, charset) {
            const strWithoutPlus = str.replace(/\+/g, ' ');
            if (charset === 'iso-8859-1') {
              // unescape never throws, no try...catch needed:
              return strWithoutPlus.replace(/%[0-9a-f]{2}/gi, unescape);
            }

            if (/^(\d+|\d*\.\d+)$/.test(str)) {
              return parseFloat(str)
            }

            const keywords = {
              true: true,
              false: false,
              null: null,
              undefined,
            }
            if (str in keywords) {
              return keywords[str]
            }

            // utf-8
            try {
              return decodeURIComponent(strWithoutPlus);
            } catch (e) {
              return strWithoutPlus;
            }
          }
})

With some ideas from previous answers, I ended up using this function to consider undefined values as well

const parseBool = (params) => {
 return !(
   params === "false" ||
   params === "0" ||
   params === "" ||
   params === undefined
 );
};

I created a package called boolean-query-express

https://www.npmjs.com/package/booleanize-query-express

The difference between it and the other packages is that it treats values as 1 and 0 as booleans and will consider params like isHere, isValid, hasSomething (camelcased).

You can read more about it as it's documented.