JSFiddle - React, Tailwind, and code Playground

JavaScript

jsonA = { "a":"1", "b":"2", "c":{"a":"1", "b":"2"} }

jsonB = { "b":"2new", "c":{"a":"1new"} }

for (var j in jsonA) {
    if(jsonB.hasOwnProperty(j)) {
        if (typeof jsonA[j] === 'object') {
            for (var i in jsonA[j]) {
                if(jsonB[j].hasOwnProperty(i)) {
                   jsonA[j][i] = jsonB[j][i];
                }
            }
        } else {
            jsonA[j] = jsonB[j];

        }
    }

}

console.log(jsonA);