A jQuery plugin template.

JQueryTemplate.plugin.js

(function ($) {

    const PLUGIN_NAME = 'myplugin'; // The name of the plugin method. (Function name of the plugin)
    const DATA_NAME = 'jqp_' + PLUGIN_NAME; // The id of the plugin instance attached to each element that this plugin was initialized on. (https://api.jquery.com/data/)

    const MyPlugin = function ($el, newOptions) {
        const _this = this;
        this.$el = $el; // Expose jQuery object this plugin is attached to.
        
        /* ---------------- Options Setup --------------- */
        this._defaults = {
            // Default options.
        };
        this._options = $.extend(true, {}, this._defaults, newOptions); // Merges options with defaults. returns new object.
        
        // If new options object is supplied it will be merged with the current options. Returns options.
        this.options = function(newOptions) { 
          return newOptions ? $.extend(true, _this._options, newOptions) : _this._options;  
        };
        
        /* ----------------- Variables ----------------- */
        
        
        /* ----------------- Functions ----------------- */
        this.demoFunction = function() {
          console.log('Hello World');
          return $el; // Return $el to make this function chainable (e.g. $('body').myplugin('demoFunction').myplugin('instance'); )  
        };
        
        this.instance = function () {
            return _this;
        };
    };


    $.fn[PLUGIN_NAME] = function (methodOrOptions, ...args) {
        let method = (typeof methodOrOptions === 'string') ? methodOrOptions : undefined;

        if (method) {

            let customPlugins = [];
            this.each(function () {
                let customPlugin = $(this).data(DATA_NAME);
                customPlugins.push(customPlugin);
            });

            let results = [];

            this.each(function (index) {
                let customPlugin = customPlugins[index];

                if (!customPlugin) {
                    console.warn('$.' + PLUGIN_NAME + ' not instantiated yet!');
                    console.info(this);
                    results.push(undefined);
                    return;
                }

                if (typeof customPlugin[method] === 'function') {
                    let result = customPlugin[method].apply(customPlugin, args);
                    results.push(result);
                } else {
                    console.warn('Method \'' + method + '\' not defined in $.' + PLUGIN_NAME);
                }
            });

            return (results.length > 1) ? results : results[0];
        } else {
            let options = (typeof methodOrOptions === 'object') ? methodOrOptions : undefined;

            return this.each(function () {
                let $el = $(this);
                let customPlugin = new MyPlugin($el, options);
                $el.data(DATA_NAME, customPlugin);
            });
        }
    }
})(jQuery);