JSFiddle - React, Tailwind, and code Playground

JavaScript

var a = {
"test123": "A",
"testing/test": "B",
"notest": "C"
};

var b = {
"test123": "Test 123",
"testing": "Testing"
};


var c = {}

    for (prop in a) {
        console.log(prop);
        propParts = prop.split("/");

        if(b.hasOwnProperty(propParts[0])) {
            c[b[propParts[0]]] = a[prop];
        } else {
            c[prop] = a[prop]
        }
    }

console.log(c);