The progress bar script that I made for my accessible form example. Works in modern browsers and IE9+. Read the blog post at http://sethlopez.me/article/understanding-accessibility-forms/.

StepProgressBar.js

/**
 * 
 * Check out the example at http://sethlopez.me/article/understanding-accessibility-forms/.
 * 
 * Copyright (c) 2015 Seth Lopez
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 *
 * Use like this:
 * 
 * HTML
 * ----------------------------------------------------------------------------
 * <ol class="steps">
 *   <li class="step">Sign In</li>
 *   <li class="step">Shipping and Payment</li>
 *   <li class="step">Gift Options</li>
 *   <li class="step">Place Order</li>
 * </ol>
 * ----------------------------------------------------------------------------
 * 
 * 
 * JS
 * ----------------------------------------------------------------------------
 * // the second argument is optional
 * var progressBar = new StepProgressBar(document.querySelector('ol.steps'), {
 *   stepSelector: 'li.step'
 * });
 * 
 * // then...
 * progressBar.next();
 * // and...
 * progressBar.previous();
 * 
 * // use a 1-based value for goToStep
 * progressBar.goToStep(1);
 * ----------------------------------------------------------------------------
 */

// polyfilled for IE9
function addClass(element, className) {
  if (element.classList) {
    element.classList.add(className);
  } else {
    element.className += ' ' + className;
  }
}

// polyfilled for IE9
function removeClass(element, className) {
  if (element.classList) {
    element.classList.remove(className);
  } else {
    element.className = element.className.replace(new RegExp('(^|\\b)' + className.split(' ').join('|') + '(\\b|$)', 'gi'), ' ');
  }
}

/**
 * Initializes an accessible "step" bar and provides and API to control it.
 *
 * @param  {HTMLElement}  progressBar  The progress bar container.
 * @param  {Object}       options      Custom options for the progress bar.
 */
function StepProgressBar(progressBar, options) {
  var defaults = {
    attrPrefix: 'data-step-',
    classPrefix: 'is-',
    completeState: 'complete',
    currentState: 'current',
    incompleteState: 'incomplete',
    initialStep: 1,
    stepSelector: 'li',
    useClasses: false,
    valueText: 'Step {{current}} of {{max}}: {{content}}'
  };

  // shallow object extend
  function extend(out) {
    out = out || {};

    for (var i = 1; i < arguments.length; i++) {
      if (!arguments[i])
        continue;

      for (var key in arguments[i]) {
        if (arguments[i].hasOwnProperty(key))
          out[key] = arguments[i][key];
      }
    }

    return out;
  }

  this.progressBar = progressBar;
  this.options = extend({}, defaults, options);
  this.steps = [].slice.call(progressBar.querySelectorAll(this.options.stepSelector));
  this.currentStep = this.options.initialStep;

  this.progressBar.setAttribute('role', 'progressbar');
  this.progressBar.setAttribute('aria-valuemin', 1);
  this.progressBar.setAttribute('aria-valuemax', this.steps.length);

  this.goToStep(this.currentStep);
}

/**
 * Takes the valueText from the progress bar options and formats it with
 * the current/max steps and a string for aria-valuetext.
 *
 * @param    {String}  content  The content to be used for aria-valuetext.
 *
 * @returns  {String}           The formatted string that can be used for
 *                              aria-valuetext.
 */
StepProgressBar.prototype.formatValueText = function format(content) {
  var valueText = this.options.valueText;

  if (!valueText || valueText.indexOf('{{content}}') === -1) {
    return content;
  }

  return valueText
    .replace(/{{current}}/ig, this.currentStep)
    .replace(/{{max}}/ig, this.steps.length)
    .replace(/{{content}}/ig, content);
};

/**
 * Sets the attribute or class state of the given element.
 *
 * @param  {HTMLElement}  element  The element to act on.
 * @param  {String}       state    The state to set.
 */
StepProgressBar.prototype.setState = function setState(element, state) {
  if (this.options.useClasses) {
    removeClass(element, this.options.classPrefix + this.options.completeState);
    removeClass(element, this.options.classPrefix + this.options.currentState);
    removeClass(element, this.options.classPrefix + this.options.incompleteState);
    addClass(element, this.options.classPrefix + state);
  } else {
    element.removeAttribute(this.options.attrPrefix + this.options.completeState);
    element.removeAttribute(this.options.attrPrefix + this.options.currentState);
    element.removeAttribute(this.options.attrPrefix + this.options.incompleteState);
    element.setAttribute(this.options.attrPrefix + state, '');
  }

  return true;
};

/**
 * Moves the progress bar to the given step.
 *
 * @param    {Number}  stepIndex  The step to move to.
 *
 * @returns  {Boolean}            Whether or not the action could be
 *                                performed.
 */
StepProgressBar.prototype.goToStep = function goToStep(stepIndex) {
  stepIndex = stepIndex - 1;

  if (stepIndex < 0 || stepIndex > (this.steps.length - 1)) {
    return false;
  }

  for (var i = 0, l = this.steps.length; i < l; i++) {
    if (i < stepIndex) {
      this.setState(this.steps[i], this.options.completeState);
    } else if (i === stepIndex) {
      this.setState(this.steps[i], this.options.currentState);
    } else if (i > stepIndex) {
      this.setState(this.steps[i], this.options.incompleteState);
    }
  }

  this.currentStep = stepIndex + 1;

  this.progressBar.setAttribute('aria-valuenow', stepIndex + 1);
  this.progressBar.setAttribute('aria-valueText', this.formatValueText(this.steps[stepIndex].textContent));

  return true;
};

/**
 * Moves the progress bar to the next step.
 *
 * @returns  {Boolean}  Whether or not the action could be performed.
 */
StepProgressBar.prototype.next = function next() {
  return this.goToStep(this.currentStep + 1);
};

/**
 * Moves the progress bar to the previous step.
 *
 * @returns  {Boolean}  Whether or not the action could be performed.
 */
StepProgressBar.prototype.previous = function previous() {
  return this.goToStep(this.currentStep - 1);
};