feat: Add JavaScript library

Add JavaScript library that includes an `icons` object, `toSvg` function and `replace` function.

src/index.js

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+/**
+ * @file Exposes `feather` object.
+ */
+
+import icons from '../dist/icons.json';
+import toSvg from './to-svg';
+import replace from './replace';
+
+module.exports = { icons, toSvg, replace };

src/replace.js

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+/**
+ * @file Implements `replace` function.
+ */
+
+/* global document, DOMParser */
+
+import icons from '../dist/icons.json';
+import toSvg from './to-svg';
+
+/**
+ * Replace all elements that have a `data-feather` attribute with SVG markup
+ * corresponding to the element's `data-feather` attribute value.
+ * @param {Object} options
+ */
+export default function replace(options = {}) {
+  if (typeof document === 'undefined') {
+    throw new Error('`feather.replace()` only works in a browser environment.');
+  }
+
+  const elementsToReplace = document.querySelectorAll('[data-feather]');
+
+  Array.from(elementsToReplace).forEach(element => replaceElement(element, options));
+}
+
+/**
+ * Replace single element with SVG markup
+ * corresponding to the element's `data-feather` attribute value.
+ * @param {Element} element
+ * @param {Object} options
+ */
+function replaceElement(element, options) {
+  const key = element.getAttribute('data-feather');
+
+  if (!key) {
+    console.error('The required `data-feather` attribute has no value.');
+    return;
+  }
+
+  if (!icons[key]) {
+    console.error(`No icon matching '${key}'. See the complete list of icons at https://feathericons.com`);
+    return;
+  }
+
+  const elementClassAttr = element.getAttribute('class');
+  const classNames = (
+    options.class ? `${options.class} ${elementClassAttr}` : elementClassAttr
+  );
+
+  const svgString = toSvg(key, Object.assign({}, options, { class: classNames }));
+  const svgDocument = new DOMParser().parseFromString(svgString, 'image/svg+xml');
+  const svgElement = svgDocument.querySelector('svg');
+
+  element.parentNode.replaceChild(svgElement, element);
+}

src/to-svg.js

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+/**
+ * @file Implements `toSvg` function.
+ */
+
+import icons from '../dist/icons.json';
+
+const DEFAULT_OPTIONS = {
+  xmlns: 'http://www.w3.org/2000/svg',
+  width: 24,
+  height: 24,
+  viewBox: '0 0 24 24',
+  fill: 'none',
+  stroke: 'currentColor',
+  'stroke-width': 2,
+  'stroke-linecap': 'round',
+  'stroke-linejoin': 'round',
+};
+
+/**
+ * Create an SVG string.
+ * @param {string} key - Icon name.
+ * @param {Object} options
+ * @returns {string}
+ */
+export default function toSvg(key, options = {}) {
+  if (!key) {
+    throw new Error('The required `key` (icon name) parameter is missing.');
+  }
+
+  if (!icons[key]) {
+    throw new Error(`No icon matching '${key}'. See the complete list of icons at https://feathericons.com`);
+  }
+
+  const combinedOptions = Object.assign({}, DEFAULT_OPTIONS, options);
+
+  combinedOptions.class = addDefaultClassNames(combinedOptions.class, key);
+
+  const attributes = optionsToAtrributes(combinedOptions);
+
+  return `<svg ${attributes}>${icons[key]}</svg>`;
+}
+
+/**
+ * Add default class names.
+ * @param {string} classNames - One or more class names seperated by spaces.
+ * @param {string} key - Icon name.
+ * @returns {string}
+ */
+function addDefaultClassNames(classNames, key) {
+  // convert class names string into an array
+  const classNamesArray = classNames ? classNames.trim().split(/\s+/) : [];
+
+  // use Set to avoid duplicate class names
+  const classNamesSet = new Set(classNamesArray);
+
+  // add default class names
+  classNamesSet.add('feather').add(`feather-${key}`);
+
+  return Array.from(classNamesSet).join(' ');
+}
+
+/**
+ * Convert options object to string of html attributes.
+ * @param {Object} options
+ * @returns {string}
+ */
+function optionsToAtrributes(options) {
+  const attributes = [];
+
+  Object.keys(options).forEach(key => {
+    attributes.push(`${key}="${options[key]}"`);
+  });
+
+  return attributes.join(' ');
+}