uso indiscriminado de setTimeout

settimeout-ruim.js

openModalSelectValues: function(product) {
    var _this = this;
    var getAttributesURL = '{{apiUrl}}/attributes?fields[attributes]=id,name&sort=name';
    var attrs = [];
    _this.configurable_product.modal.product = product;
    _this.configurable_product.modal.attributes = [];

    _this.$http.get(getAttributesURL).then((response) => {
        var attributes = response.data.data;

        attributes.forEach(function(a, k) {
            if (_.contains(_this.configurable_product.attributes.selected, a.attributes.id)) {
                attrs.push({
                    id: a.attributes.id,
                    name: a.attributes.name,
                    values: []
                });
            }
        });

        setTimeout(function() {
            attrs.forEach(function(a) {
                var getAttributeValuesURL = '{{apiUrl}}/attributes/' + a.id + '/values';
                _this.$http.get(getAttributeValuesURL).then((response) => {
                    var values = response.data.data;
                    // a.values = values;
                    values.forEach(function(v, k) {
                        a.values.push({
                            id: v.attributes.id,
                            name: v.attributes.name
                        });
                    });

                    a.values = _.uniq(a.values);
                }, (response) => {});
            });
        }, 300);

    }, (response) => {});

    $('select#configurable_product-attribute-values').empty();

    setTimeout(function() {
        _.uniq(attrs).forEach(function(a) {
            var optgroup = $('<optgroup>');
            optgroup.attr('label', a.name);

            a.values.forEach(function(v) {
                var option = $("<option>");
                option.val(v.id);
                option.text(v.name);

                optgroup.append(option);
            });

            $('select#configurable_product-attribute-values').append(optgroup);
        });
        $('select#configurable_product-attribute-values').multiselect('rebuild');
    }, 600);

    $('#modal-select-values').modal('show');
}