passing $scope variable to a function in AngularJS

Question

I've been trying to create a generic function in angular that changes a $scope parameters value.

I've been wondering why I cannot pass $scope.var as an argument to a function e.g.:

webApp.controller ('VotesCtrl', function ($scope) {
    $scope.param = 42;

    change($scope.param);
    function change(contextParam) {
      contextParam = (Math.random()*100)+1;
    };
});

When I ran this function $scope.param remains 42.

Is there an alternative besides:

webApp.controller ('VotesCtrl', function ($scope) {
    $scope.param = 42;

    change('param');
    function change(contextParam) {
      $scope[contextParam] = (Math.random()*100)+1;
    };
});

My Plunk

To understand why plnkr.co/edit/9996W3Io4KewA3tgokQR?p=preview is not working. And if the solution I gave is the only way — Canttouchit
– Canttouchit, Commented Mar 19, 2014 at 15:41
I would avoid passing around scoped Items like this, if you need to pass it into a function I would define it locally and pass that in. If you wanted to change the scoped value then you could just call the scoped item inside the function without a need to pass it in. — Mindstormy
– Mindstormy, Commented Mar 19, 2014 at 15:42

Ian Mercer · Accepted Answer · 2014-03-19 15:40:38Z

6

The short answer is "Don't bind to primitive values". See http://stsc3000.github.io/blog/2013/10/26/a-tale-of-frankenstein-and-binding-to-service-values-in-angular-dot-js/

var webApp = angular.module('webApp', []);

//controllers
webApp.controller ('VotesCtrl', function ($scope) {
    $scope.param = { value: 42 };

    change($scope.param);
    function change(contextParam) {
      contextParam.value = (Math.random()*100)+1;
    };
});

answered Mar 19, 2014 at 15:40

Ian Mercer

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1 Comment

redfox05 Over a year ago

Or you pass the entire $scope object to the function instead. Not keen on passing scope or its attributes around, so either option is not great imo.

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