Check if a key exists inside a JSON object

Try this

if (thisSession.hasOwnProperty("merchant_id")) {

}

the JS Object thisSession should be like

{
  amt: "10.00",
  email: "[email protected]",
  merchant_id: "sam",
  mobileNo: "9874563210",
  orderID: "123456",
  passkey: "1234"
}

you can find the details here

There's several ways to do it, depending on your intent.

thisSession.hasOwnProperty('merchant_id'); will tell you if thisSession has that key itself (i.e. not something it inherits from elsewhere)

"merchant_id" in thisSession will tell you if thisSession has the key at all, regardless of where it got it.

thisSession["merchant_id"] will return false if the key does not exist, or if its value evaluates to false for any reason (e.g. if it's a literal false or the integer 0 and so on).

(I wanted to point this out even though I'm late to the party)
The original question you were trying to find a 'Not IN' essentially. It looks like it is not supported by the research (2 links below) that I was doing.

So if you wanted to do a 'Not In':

    ("merchant_id" in x)
    true
    ("merchant_id_NotInObject" in x)
    false 

I'd recommend using the ! operator

    if (!("merchant_id" in thisSession))
    {
        // do nothing.
    }
    else 
    {
        alert("yeah");
    }

https://linuxhint.com/use-not-in-operator-javascript/

you can do like this:

if("merchant_id" in thisSession){ /** will return true if exist */
 console.log('Exist!');
}

or

if(thisSession["merchant_id"]){ /** will return its value if exist */
 console.log('Exist!');
}

Type check also works :

if(typeof Obj.property == "undefined"){
    // Assign value to the property here
    Obj.property = someValue;
}

This code causes esLint issue: no-prototype-builtins

foo.hasOwnProperty("bar") 

The suggest way here is:

Object.prototype.hasOwnProperty.call(foo, "bar");

I change your if statement slightly and works (also for inherited obj - look on snippet)

if(!("merchant_id" in thisSession)) alert("yeah");

var sessionA = {
  amt: "10.00",
  email: "[email protected]",
  merchant_id: "sam",
  mobileNo: "9874563210",
  orderID: "123456",
  passkey: "1234",
}

var sessionB = {
  amt: "10.00",
  email: "[email protected]",
  mobileNo: "9874563210",
  orderID: "123456",
  passkey: "1234",
}


var sessionCfromA = Object.create(sessionA); // inheritance
sessionCfromA.name = 'john';


if (!("merchant_id" in sessionA)) alert("merchant_id not in sessionA");
if (!("merchant_id" in sessionB)) alert("merchant_id not in sessionB");
if (!("merchant_id" in sessionCfromA)) alert("merchant_id not in sessionCfromA");

if ("merchant_id" in sessionA) alert("merchant_id in sessionA");
if ("merchant_id" in sessionB) alert("merchant_id in sessionB");
if ("merchant_id" in sessionCfromA) alert("merchant_id in sessionCfromA");

JavaScript changes once again!

(TL;DR: Use Object.hasOwn now.)

The long standing highest-voted answer recommends using hasOwnProperty. This was the best answer at the time, but it does have a number of tricky bits that can trip you up. For example, if the variable can be null, this will cause a TypeError when you attempt to call hasOwnProperty. Less commonly (but a symptom of the same problem), if an object could potentially have a key named "hasOwnProperty," that would shadow the function you wanted. (This could be a problem if, for example, you are parsing user-provided input.)

Because of all that, the previously correct way to call the function is this mess:

Object.prototype.hasOwnProperty.call(thisSession, "merchant_id");

In updated browsers and recent versions of node there is a new alternative that addresses these problems. Object now has a static method named hasOwn that addresses these pitfalls.

Object.hasOwn(thisSession, "merchant_id")

Ahh, much better. :)

If you are targeting browsers or node versions new enough to have hasOwn, you should stop using hasOwnProperty entirely. It is obsolete.

function to check undefined and null objects

function elementCheck(objarray, callback) {
        var list_undefined = "";
        async.forEachOf(objarray, function (item, key, next_key) {
            console.log("item----->", item);
            console.log("key----->", key);
            if (item == undefined || item == '') {
                list_undefined = list_undefined + "" + key + "!!  ";
                next_key(null);
            } else {
                next_key(null);
            }
        }, function (next_key) {
            callback(list_undefined);
        })
    }

here is an easy way to check whether object sent is contain undefined or null

var objarray={
"passenger_id":"59b64a2ad328b62e41f9050d",
"started_ride":"1",
"bus_id":"59b8f920e6f7b87b855393ca",
"route_id":"59b1333c36a6c342e132f5d5",
"start_location":"",
"stop_location":""
}
elementCheck(objarray,function(list){
console.log("list");
)

we can use lodash library

import _ from 'lodash';

if(_.isEmpty(merchant_id)){
    // do nothing
}
else{
    //do something with merchant id
}