javascript - Why doesn't this function run when the reactive variable changes value? -

i'm new meteor , i'm trying hang of whole reactivity thing.

there isn't specifc reason why want function re-run, in fact, not re-running desired behavior use case. want know why happening can better understand concepts.

if add function property on template instance, this:

template.services.oncreated( function() {     this.templates = [         "web_design",         "painting",         "gardening"     ];     this.current_index = new reactivevar(0);      this.determineslidedirection = function() {         console.log(this.current_index.get());     }; }); 

and update reactive var in response event.

template.services.events({     'click .nav-slider .slider-item': function(event, template) {         var new_selection = event.currenttarget;         template.current_index.set($(new_selection).index());     } }); 

the function not re-run upon invocation of set() call.

however, if have helper utilizes variable, re-run.

template.services.helpers({     currenttemplate: function() {         var self = template.instance();         return self.templates[self.current_index.get()];     } }); 

why this?

reactive data sources cause functions automatically re-run. these functions are:

• tracker.autorun
• template.mytemplate.helpers({})
• blaze.render , blaze.renderwithdata

in code above want use tracker.autorun

template.services.oncreated( function() {     this.templates = [         "web_design",         "painting",         "gardening"     ];      this.current_index = new reactivevar(0);      tracker.autorun(function(){         // actually, might not work because context of         // 'this' might changed when inside of tracker.         this.determineslidedirection = function() {             console.log(this.current_index.get());         };     }); });