src/observable-hash.js
function(expression, onChange, callbackContext) {
    var observer = this._observations.createObserver(expression, onChange, callbackContext || this);
    this._observers.push(observer);
    if (this.observersEnabled) observer.bind(this._context);
    return observer;
  }
function(expression, onChange, callbackContext) {
    var observer = this._observations.createObserver(expression, onChange, callbackContext || this);
    this._observers.push(observer);
    if (this.observersEnabled) observer.bind(this._context);
    return observer;
  }
function ( expression , onChange , callbackContext ) { var observer = this . _observations . createObserver ( expression , onChange , callbackContext || this ) ; this . _observers . push ( observer ) ; if ( this . observersEnabled ) observer . bind ( this . _context ) ; return observer ; }
Watch this object for changes in the value of the expression
@param {String} expression The expression to observe
@param {Function} onChange The function which will be called when the expression value changes
@return {Observer} The observer created
Watch this object for changes in the value of the expression