Question

How does this code read for reading through an object, able to read objects within it:

var book = {
    "main title": "Javascript",
    "sub-title": "Def Guide",
    "for": "all audiences",
    author: {
        firstname: "David",
        surname: "Fatagans"
    }
};

for (propName in book){
    console.log("key: " + propName + " value: " + book[propName]);
    if (typeof book[propName] === "object"){
        for (innerObject in book[propName]){
            console.log("key: " + innerObject + "value: " + book[propName][innerObject])
        }
    }
}

Answer 1

One way is to put the code into a function and call it recursively, something like:

function printObject(obj) {
  for (var propName in obj) {
    console.log("key: " + propName + " value: " + obj[propName]);

    if (typeof obj[propName] == "object") {
        printObject(obj);
    }
  }
}

The above will also show enumerable attributes on the object’s [[Prototype]] chain. To ignore those, use a hasOwnProperty test:

  if (obj.hasOwnProperty(propName)) {
    // propName is not inherited
  }

Be careful with passing host objects (e.g. DOM elements) to the function, extra precautions need to be taken with those.