angularjs - How does $parse work? -

i have simple code this:

<div ng-app="app">   <input type="text" ng-model="money" mask="2">   <p>{{money}}</p> </div>  angular.module("app", [])   .directive("mask", function($parse) {     return {       restrict: "a",       require: "ngmodel",       link: function(scope, element, attrs) {         console.log($parse(attrs.mask)); // function(s, l, a, i){return 2;}         console.log($parse(attrs.mask)(scope)); // 2       }     }   }); 

why first output function(s, l, a, i){return 2;}with (s, l, a, i)?

in case need jsfiddle: https://jsfiddle.net/ealonwang/x1hcbpjw/11/

according angular documentation $parse service

$parse() without calling scope iief, returns function evaluated expession, aka: return 2;

however function returned takes multiple arguments:

function(context, locals) function represents compiled expression:

context – {object} – object against expressions embedded in strings evaluated against (typically scope object). locals – {object=} – local variables context object, useful overriding values in context.

the returned function has following properties:

literal – {boolean} – whether expression's top-level node javascript literal. constant – {boolean} – whether expression made entirely of javascript constant literals. assign – {?function(context, value)} – if expression assignable, set function change value on given context.

so seeing evaluated not invoked function being returned service.

listed below test cases ran against service explain how locals , context used , defined:

var getter = $parse('user.name'); var setter = getter.assign; var context = {user:{name:'angular'}}; var locals = {user:{name:'local'}};  expect(getter(context)).toequal('angular'); setter(context, 'newvalue'); expect(context.user.name).toequal('newvalue'); expect(getter(context, locals)).toequal('local'); 

specifically arguments mean found here: https://github.com/angular/angular.js/blob/master/src/ng/parse.js#l1934

var value = parsedexpression(scope, locals, assign, inputs);