browser.js

'use strict';
// For more information about browser field, check out the browser field at https://github.com/substack/browserify-handbook#browser-field.

var styleElementsInsertedAtTop = [];

var insertStyleElement = function(styleElement, options) {
    var head = document.head || document.getElementsByTagName('head')[0];
    var lastStyleElementInsertedAtTop = styleElementsInsertedAtTop[styleElementsInsertedAtTop.length - 1];

    options = options || {};
    options.insertAt = options.insertAt || 'bottom';

    if (options.insertAt === 'top') {
        if (!lastStyleElementInsertedAtTop) {
            head.insertBefore(styleElement, head.firstChild);
        } else if (lastStyleElementInsertedAtTop.nextSibling) {
            head.insertBefore(styleElement, lastStyleElementInsertedAtTop.nextSibling);
        } else {
            head.appendChild(styleElement);
        }
        styleElementsInsertedAtTop.push(styleElement);
    } else if (options.insertAt === 'bottom') {
        head.appendChild(styleElement);
    } else {
        throw new Error('Invalid value for parameter \'insertAt\'. Must be \'top\' or \'bottom\'.');
    }
};

module.exports = {
    // Create a <link> tag with optional data attributes
    createLink: function(href, attributes) {
        var head = document.head || document.getElementsByTagName('head')[0];
        var link = document.createElement('link');

        link.href = href;
        link.rel = 'stylesheet';

        for (var key in attributes) {
            if ( ! attributes.hasOwnProperty(key)) {
                continue;
            }
            var value = attributes[key];
            link.setAttribute('data-' + key, value);
        }

        head.appendChild(link);
    },
    // Create a <style> tag with optional data attributes
    createStyle: function(cssText, attributes, extraOptions) {
        extraOptions = extraOptions || {};

        var style = document.createElement('style');
        style.type = 'text/css';

        for (var key in attributes) {
            if ( ! attributes.hasOwnProperty(key)) {
                continue;
            }
            var value = attributes[key];
            style.setAttribute('data-' + key, value);
        }

        if (style.sheet) { // for jsdom and IE9+
            style.innerHTML = cssText;
            style.sheet.cssText = cssText;
            insertStyleElement(style, { insertAt: extraOptions.insertAt });
        } else if (style.styleSheet) { // for IE8 and below
            insertStyleElement(style, { insertAt: extraOptions.insertAt });
            style.styleSheet.cssText = cssText;
        } else { // for Chrome, Firefox, and Safari
            style.appendChild(document.createTextNode(cssText));
            insertStyleElement(style, { insertAt: extraOptions.insertAt });
        }
    }
};