[removed] Determine unknown array length and map dynamically

Question

Going to do my best at explaining what I am trying to do.

I have two models, mine and an api response I am receiving. When the items api response comes in, I need to map

Answer 1

So you have defined a little language to define some data addressing and manipulation rules. Let's think about an approach which will allow you to say

access(apiPath, function(value) { insert(myPath, value); }

The access function finds all the required items in apiPath, then calls back to insert, which inserts them into myPath. Our job is to write functions which create the access and insert functions; or, you could say, "compile" your little language into functions we can execute.

We will write "compilers" called make_accessor and make_inserter, as follows:

function make_accessor(program) {

  return function(obj, callback) {

    return function do_segment(obj, segments) {
      var start    = segments.shift()             // Get first segment
      var pieces   = start.match(/(\w+)(\[\])?/); // Get name and [] pieces
      var property = pieces[1];
      var isArray  = pieces[2];                   // [] on end
      obj          = obj[property];               // drill down

      if (!segments.length) {                     // last segment; callback
        if (isArray) {
          return obj.forEach(callback);
        } else {
          return callback(obj);
        }
      } else {                                    // more segments; recurse
        if (isArray) {                            // array--loop over elts
          obj.forEach(function(elt) { do_segment(elt, segments.slice()); });
        } else {
          do_segment(obj, segments.slice());      // scalar--continue
        }
      }
    }(obj, program.split('.'));
  };
}

We can now make an accessor by calling make_accessor('items[].name').

Next, let's write the inserter:

function make_inserter(program) {

  return function(obj, value) {

    return function do_segment(obj, segments) {
      var start    = segments.shift()             // Get first segment
      var pieces   = start.match(/(\w+)(\[\])?/); // Get name and [] pieces
      var property = pieces[1];
      var isArray  = pieces[2];                   // [] on end

      if (segments.length) {                      // more segments
        if (!obj[property]) {
          obj[property] = isArray ? [] : {};
        }
        do_segment(obj, segments.slice());
      } else {                                    // last segment
        obj[property] = value;
      }
    }(obj, program.split('.'));
  };
}

Now, you can express your whole logic as

access = make_accessor('items[].name');
insert = make_inserter('outputModel.items[].uniqueName');

access(apiPath, function(val) { insert(myPath, val); });