isSalesforce1() JavaScript function

is-salesforce1.js

/*
 * @return whether JavaScript is executing
 *         within the context of Salesforce1.
 *         If not, the context is assumed
 *         to be the regular browser "app".
 */
function isSalesforce1() {
  
  // Use the presence of sforce.one
  // as the acid test to know that
  // the code is running in Salesforce1.
  // Assume sforce.one is absent
  // unless it's detected.
  var hasSforceOne = false;
  
  // Follow best practices recommended
  // by Mozilla to test for presence
  // of sforce.one: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined
  if (typeof sforce !== 'undefined') {
    if (typeof sforce.one !== 'undefined')
      hasSforceOne = true;
  }
  
  // Return presence or absence
  // of sforce.one as the result
  return hasSforceOne;
}