Function to change the text of a button using textContent with a fallback for old browsers

change-button-text.js

 /* Try it at Codepen.io - http://codepen.io/seantunwin/pen/aDsHE */

/**
 * Change the text of a button
 * @param {el} object HTMLElement: button to change text of
 * @param {dText} string: default text
 * @param {nText} string: new text
 **/
function changeText(el, dText, nText) {
  var content = '',
      context = '';
  
  /* Check to see if the browser accepts textContent */
  if ('textContent' in document.body) {
    context = 'textContent';
    /* Get the current button text */
    content = el[context];
  /* Browser does NOT use textContent */
  } else {
    /* Get the button text with fallback option */
    content = el.firstChild.nodeValue;
  }
  
  /* Set button text */
  if (context === 'textContent') {
    el.textContent = (content === dText) ? nText : dText;
  } else {
    el.firstChild.nodeValue = (content === dText) ? nText : dText;
  }
}

/* Default text of the button */
var defaultText = 'Change';
/* Alternate text for button */
var substituteText = 'Revert';

/* Grab our button */
var btn = document.querySelector('.btn');

/* Add a listener to the button instance so we can manipulate it */
btn.addEventListener('click', function() {
  changeText(this, defaultText, substituteText);
}, false);