[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

I have borrowed earlier answer and made improvements so as to solve both your examples and this should be generic. Though if you plan to run this sequencially with 2 sets of inputs, then the behavior will be as I have outlined in my comments to your original question.

    var apiObj = {
    items: [{
        name: "Hammer",
        skus: [{
            num: "12345qwert"
        }]
    }, {
        name: "Bike",
        skus: [{
            num: "asdfghhj"
        }, {
            num: "zxcvbn"
        }]
    }, {
        name: "Fork",
        skus: [{
            num: "0987dfgh"
        }]
    }]
};

var myObj = { //Previously has values
    storeName: "",
    items: [{
        uniqueName: ""
    }],
    outputModel: {
        items: [{
            name: "Hammer"
        }]
    }
};

/** Also works with this **
var myPath = "outputModel.items[].uniqueName";
var apiPath = "items[].name";
*/
var myPath = "outputModel.items[].sku";
var apiPath = "items[].skus[].num";

function make_accessor(program) {

    return function (obj, callback) {
        (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('.'));
    };
}

function make_inserter(program) {

    return function (obj, value) {
        (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[property], segments.slice());
            } else { // last segment
                if (Array.isArray(obj)) {
                    var addedInFor = false;
                    for (var i = 0; i < obj.length; i++) {
                        if (!(property in obj[i])) {
                            obj[i][property] = value;
                            addedInFor = true;
                            break;
                        }
                    }
                    if (!addedInFor) {
                        var entry = {};
                        entry[property] = value;
                        obj.push(entry);
                    }
                } else obj[property] = value;
            }
        })(obj, program.split('.'));
    };
}

access = make_accessor(apiPath);
insert = make_inserter(myPath);

access(apiObj, function (val) {
    insert(myObj, val);
});

console.log(myObj);