$parse and $eval [Angular]

$parse and $eval both operate on angular expressions i.e. {{ expression }}.

$eval is a scope method which executes an expression on the current scope and returns the result.

 scope.a = 1;   
 scope.b = 2;   
 scope.$eval('a+b'); // 3  

$parse is an Angular service which converts an expression into a function. Then function can be invoked and passed a context (usually scope) in order to retrieve the expression's value.

 <div my-attr="obj.name" my-directive> theprogrammingtree.com </div>   
 <script type="text/javascript">   
 myApp.directive('myDirective', function( $parse, $log ) {   
    return function( scope, el, attrs ) {  
      // parse the "my-attr" attribute value into a function   
      var myFn = $parse( attrs.myAttr );   
      // "myFn" is now a function which can be invoked to get the expression's value;   
      // the following line logs the value of obj.name on scope:   
       $log.log(myFn(scope) );   
      // theprogrammingtree.com   
      el.bind('click', function() {   
        // "myFn.assign" is also a function; it can be invoked to   
        // update the expresssion value   
        myFn.assign(scope, "New name");   
        scope.$apply();   
      })   
    }   
 });   
 </script>  

Also, if the expression is assignable then the returned function will have an assign property. The assign property is a function that can be used to change the expression's value on the given context.