Create cartesian product (powerset?) of JavaScript objects by looping through unknown number of arrays

Question

I'm a beginner, so please pardon my ignorance if this is trivial.

I have a javascript object of unknown length, and each property's value is an array (also of unknown length to me). For example:

var obj = {"varA":[1,2,3],
           "varB":['good','bad'],
           "varC":[0,100],
           "varD":['low','med','high']
          }

I want to loop through each of the properties and create a new object for every combination of property values. If I knew the number of properties I could just brute-forcedly use for loops, but is there a way to enumerate without knowing how many loops to hard-code?

I essentially want to do this kind of thing:

var oblist = [];
for (a in varA){
 for (b in varB){
  for (c in varC){
   for (d in varD){
    oblist.push({"varA":varA[a], "varB":varB[b], "varC":varC[c], "varD":varD[d]});
   }
  }
 }
}

so that oblist will contain objects like:

{"varA":1, "varB":"good", "varC":0, "varD":"low"}
{"varA":1, "varB":"good", "varC":0, "varD":"med"}
...
{"varA":3, "varB":"bad", "varC":100, "varD":"high"}

Thanks!

Edit: Look I'm not asking for for-loop or indexing syntax help. I'm asking what to do if I don't know the number of properties in the object (e.g. varA, varB, varC, varD, varE, hell i could have varZZ for all i know), so I can't just hard-code 4 for loops. Is there a way to set that using obj[Object.keys(obj)[i]].length?

Answer 1

var obj = {"varA":[1,2,3],
           "varB":['good','bad'],
           "varC":[0,100],
           "varD":['low','med','high']
          }
 
// flatten the object into an array so it's easier to work with
var obj2list = function(obj) {
  var list = [];
  for (var key in obj) {
    if (obj.hasOwnProperty(key)) {
      list.push({
        name: key,
        val: obj[key]
      });
    }
  }
  return list;
};
 
// implement your favorite version of clone...this isn't particular fast
var cloneObj = function(obj) {
  return JSON.parse(JSON.stringify(obj));
}
 
var iterateAndPopulateCombo = function(currentObj, listToIterate, result) {
  if (listToIterate.length == 0) {
    result.push(currentObj);
  } else {
    listToIterate[0].val.forEach(function(d) {
      var newObj = cloneObj(currentObj);
      newObj[listToIterate[0].name] = d;
      iterateAndPopulateCombo(newObj, listToIterate.slice(1), result);
    })
  }
}
 
var list = obj2list(obj);
var result = [];
iterateAndPopulateCombo({}, list, result);
console.log(JSON.stringify(result));
document.body.appendChild(document.createTextNode(JSON.stringify(result)));