getElementByClassName

getElementByClassName.js

function isArray(target) {
  return Object.prototype.toString.call(target) === "[object Array]";
}

function isClassSelector(selector) {
  return /^\.[\w-]+$/.test(selector);
}

function getSelector(array) {
  if (!array || !array.length) return;

  var selectors = [];

  array.forEach(function(item) {
    if (typeof item === "string") {
      if (isClassSelector(item)) {
        selectors.push(item);
      }
    } else if (isArray(item)) {
      [].forEach.call(item, function(sel) {
        if (isClassSelector(sel)) {
          selectors.push(sel);
        }
      });
    }
  });

  return selectors;
}

function recursive(node, selector, result) {
  if (node.nodeType === Node.ELEMENT_NODE) {
    var classNames = node.className.split(" ");

    if (classNames && classNames.length) {
      for (var i = 0; i < classNames.length; i++) {
        var cn = classNames[i];
        if (selector.indexOf("." + cn) !== -1) {
          result.push(node);
          break;
        }
      }
    }

    if (node.children && node.children.length) {
      [].forEach.call(node.children, function(node) {
        recursive(node, selector, result);
      });
    }
  }
}

function getElementByClassName() {
  var selectors = getSelector([].slice.call(arguments));

  if (!selectors || !selectors.length) return;

  var result = [];

  var rootNode = document.documentElement;

  recursive(rootNode, selectors, result);

  return result;
}