Make option groups from WordPress API Categories list

wordpress_api_option_groups_categories.js

var categories = getCategories(); // this function gets the categories with ajax (you'll have to do that yourself ;-))
var html = "";

var tpl_categories = []; // top level categories
var top_cat_count = 0;

for (i = 0; i < categories.length; i++) {

  if ( categories[i].parent == 0 ) {

    tpl_categories[top_cat_count] = categories[i];

    var sub_cat_count = 0;

    for (sub_i = 0; sub_i < categories.length; sub_i++) {

      if ( categories[sub_i].parent == categories[i].id ) {


        if ( "sub_categories" in tpl_categories[top_cat_count] == false ) {
          tpl_categories[top_cat_count].sub_categories = [];
        }

        tpl_categories[top_cat_count].sub_categories[sub_cat_count] = categories[sub_i];

        sub_cat_count++;
      }

    }

    top_cat_count++;

  }
}

for (i = 0; i < tpl_categories.length; i++) {

  if ( "sub_categories" in tpl_categories[i] ) {
    html += '<optgroup label="'+tpl_categories[i].name+'">';

    for ( sub_i = 0; sub_i < Object.keys(tpl_categories[i].sub_categories).length; sub_i++ ) {
      html += '<option value="'+tpl_categories[i].sub_categories[sub_i].id+'">'+tpl_categories[i].sub_categories[sub_i].name+'</option>';
    }

    html += '</optgroup>';
  } else {
    html += '<option value="'+tpl_categories[i].id+'">'+tpl_categories[i].name+'</option>';
  }

}

//console.log(html);
//$('select').html(html);