When to use $parse in Angular.js

Question

How does the $parse provider in angular js work, In which cases would it be useful and in which cases would the assign fn be available.

Answer 1

$parse is useful for evaluating a string and returning a function that can manipulate a model, or call a function. Any variables within the string is resolved from the context that is passed into the function.

Getting and Setting a Property of a Model

$parse is useful for compiling an angular expression into a function that can get/set a model.

For example, if you want to get/set user.name, you can use $parse('user.name'):

Getter

var context = { user: { name: 'john'}};
var getter = $parse('user.name');
var name = getter(context);
console.log(name); // outputs 'john'

Setter

var context = { user: { name: 'john'}};
var setter = $parse('user.name').assign;
setter(context, 'tom');
console.log(context.user.name); //outputs tom

$scope can also serve as the context:

$scope.user = { name: 'john' };
var getter = $parse('user.name');
var name = getter($scope);
console.log(name); // outputs 'john'

Calling a Function

$parse may also be used to compile an angular expression into a callable function.

For example, if you want to call a function called helloWorld():

var context = { 
      helloWorld: function(name) { 
           alert(name); 
      }, 
      user: {
           name:'john'
      }
};
var fn = $parse('helloWorld(user.name)');
fn(context); // alerts 'john'

Answer 2

You want to use $parse when you want to convert angular expression into javascript function. Angular expression is a string such as {{ expression }}.

Take a look at this article. $parse