CSS media query in javascript using bootstrap classes

index.js

/**
 * User: TimAnderson
 * Date: 12/1/15
 * Time: 1:25 PM
 */

/**
 * Test responsive screen sizes by creating a visible-[screen]-block div. Passing multiple screen sizes will return true if one of them is true.
 * See {@link http://codepen.io/mindfullsilence/pen/BjRJvN} for example usage.
 * @requires jQuery
 * @param {(...string|array)} className - The screen(s) to check against. In bootstrap, these are 'xs', 'sm', 'md', 'lg'.
 * @returns {Boolean}
 */

const $ = require('jquery')

const mediaIs = function ( className ) {
    var class_string = '',
        $item,
        visible;
    var stringcheck = function(item) {
        var allowed = ['xs', 'sm', 'md', 'lg'];
        if(allowed.indexOf(item) === -1) {
            console.warn('mediaIs: The string you passed ("' + item + '") does not match one of [' + allowed.join(',') + '], which are the bootstrap default screen sizes. Unless you have created a .visible-' + item + '-block class in your styles, this will likely return a false positive.');
            console.trace();
        }
    };

    if ( className instanceof Array ) {
        className.forEach( function ( el, index ) {
            if(typeof el === 'string') {
                stringcheck(el);
                class_string += 'visible-' + el.trim() + '-block ';
            }
            else {
                console.error('mediaIs: Index ' + index + ' of your array must be a string. You passed in ' + typeof el + '.');
            }
        } )
    }
    else if ( arguments.length > 1 ) {
        [].slice.call( arguments ).forEach( function ( el ) {
            if ( typeof el === 'string' ) {
                stringcheck( el );
                class_string += 'visible-' + el.trim() + '-block ';
            }
            else {
                console.error( 'mediaIs: ' + [].slice.call( arguments ).join( ', ' ) + ' cannot be used in this method because it is of type ' + typeof className );
                return false;
            }
        } );
    }
    else if ( typeof className === 'string' ) {
        stringcheck(className);
        class_string += 'visible-' + className + '-block';
    }
    else {
        console.error( 'mediaIs: ' + [].slice.call( arguments ).join( ', ' ) + ' cannot be used in this method because it is of type ' + typeof className + '.\nYou may use a string only.');
        return false;
    }

    $item = $( '<div class="' + class_string + '"></div>' );
    $( 'body' ).append( $item );
    visible = ($item.css( 'display' ) != 'none');
    $item.remove();
    return visible;
};

module.exports = mediaIs

package.json

{
  "name": "mediaIs",
  "description": "Check the current screen size against bootstrap classes",
  "version": "1.0.0",
  "repositories": [
    {
      "type": "git",
      "url": "https://gist.github.com/06db84f0992e165a3b01.git"
    }
  ],
  "licenses": [
    {
      "name": "MIT",
      "url": "https://opensource.org/licenses/MIT"
    }
  ],
  "dependencies" : { 
    "jquery" : ">=2.0.0"
  }
}