something, that lodash already does

key-in-json.js

var pc = '',
    ERROR = 'Not found';

// something doing with pc

function getKeyInJson(path, json) {
    var key;

    if (path === '') {
        return JSON.stringify(pc);
    }

    if (typeof path === 'string') {
        path = path.split('/');
    }
    key = path.shift();

    if (typeof json[key] === 'undefined') {
        return ERROR;
    }

    return path.length ?
        getKeyInJson(path, json[key]) :
        JSON.stringify(json[key]);
}