Information about autorun function

help
1

Currently reading about FlowRouter. Faced with example with autorun function and can’t find good explanation. Also want to understand what object ‘this’ will be. Please help with useful links.

Template.blogPost.onCreated(function() { var self = this; self.autorun(function() { var postId = FlowRouter.getParam('postId'); self.subscribe('singlePost', postId); }); });

2

Tracker.autorun(…) allows converting a piece of code into reactive code when the source data it relays on changes.

According to the Meteor documentation, .onCreated is a Template method, so “this” is bound to a template instance object that is unique to this inclusion of the template and remains across re-renderings… not sure how in the code you pasted can do .autorun(…). I’d like to know too.

3

Thank you, it was really helpful. Few minutes ago have found nice link about autorun and realization of it http://stackoverflow.com/questions/30546486/in-plain-english-what-does-tracker-autorun-do

4

Also the following simple code can help you understand better what Tracker.autorun(…) does:

Meteor.startup(function() {
  Tracker.autorun(function() {
    console.log('There are ' + Posts.find().count() + ' posts');
  });
});

In this case, Tracker.autorun() is making the console to automatically display the “There are X posts” message whenever the posts collection changes, where X is the number of posts in the collection. This is pretty cool since it saves you lots of lines of code.

2 Likes
5

If you invoke autorun on a template instance, the autorun will automatically be stopped when the template is destroyed.

Btw nowadays you can just do

Template.blogPost.onCreated(function () {
    this.autorun(() => {
        const postId = FlowRouter.getParam('postId');
        this.subscribe('singlePost', postId);  
    });
});
6

But which object does “this” in that context represent? The template instance? or the tracker?

7

this.autorun -> this refers to the template instance
Then the ES2015 arrow function notation binds the parent scope, so you don’t have to do the var self = this dance.

8

But what I don’t understand is that if .autorun is a method of Tracker, how can you access it from the template instance (self).

9

Check out this line from the blaze package from meteor core: https://github.com/meteor/meteor/blob/devel/packages/blaze/template.js#L321

1 Like
10

Got it now, thanks for your help.