Handlebars - {{#each}} over an array with null values - is it correct that it bombs?

[Daniel Dornhardt]

Hello,

i'm pretty new to meteor.js, so 1st: Thank you to the devs, this is more awesome than awesome!

I'm trying to get my feet wet and I just stumbled over this issue:

When I try to {{#each}} over an array containing a null value I get the following errors:

In the browser console:

Uncaught TypeError: Cannot read property '_id' of null

Exception from Meteor.flush: TypeError: Cannot call method 'firstNode' of undefined

Seeing that the handlebars documentation states that {{#if }} can be used to test against null, I would have expected an array to be able to contain null values...

Or am I not getting something here?

Is it a handlebars thing or something meteor-Specific?

[David Ascher]

Hard to know without seeing more code, but that looks like you're iterating over an array of nulls, and then looking for the _id property of the thing in the array.  So likely your helper or template variable needs to check that its input isn't null.

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[Daniel Dornhardt]

Hello,

yes, I can work around the issue now that I know it exists, but it might be a bug or an inconsistency introduced by meteor maybe?

This is the minimal example:

Template:

<template name="example">

    <ul>

        {{#each exampleList}}

            <li>{{this}}</li>

        {{/each}}

    </ul>

</template>

JS:

Works:

Template.example.exampleList = function() {

    return ['one', 'two', 'three'];

};

Breaks:

Template.example.exampleList = function() {

    return ['one', 'two', 'three', null];

};

I just wouldn't expect my Program to fail because of a null value in an array?

Thanks and best wishes

Daniel

[Daniel Dornhardt]

Hello once more,

it seems to work with handlebars alone: http://jsfiddle.net/mvdxn/ (Even though that uses a slightly older version of handlebars, my github-fu isn't too good).

My guess is that meteor is trying to look for bound data in the data structure somehow, and that doesn't work with null properties somehow?

Just curious

Daniel

[Chris Mather]

Hi Daniel,

The reason for this can be found on line 38 of packages/handlebars/evaluate.js where the Handlebars 'each' method is implemented. For each item of your array, Meteor is creating a branch label Spark annotation using the "_id" property of the item, the item itself, or a Spark.UNIQUE_LABEL. This is so that Meteor can find the row later if/when the data changes (in a reactive data source, not a plain array). I probably should have done one more Spark screencast on labels but decided to skip it for now.

I haven't completely thought through the implications, but the 'each' code should probably be guarding against a null item in the array but it currently isn't. So that's why you're seeing that exception.

Chris

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[Chris Mather]

If you're curious, I forgot to mention the reactive implementation of 'each' is in packages/templating/deftemplate.js on line 21. But same basic issue - not guarding against a null item.

C

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[Ken Yee]

On Wednesday, March 6, 2013 2:00:11 PM UTC-5, Chris Mather wrote:

I haven't completely thought through the implications, but the 'each' code should probably be guarding against a null item in the array but it currently isn't. So that's why you're seeing that exception.

This was something I hit a week or two back as well...not very intuitive, so IMHO, it's a bug that should be fixed.
Most other templating systems treat unknowns/nulls as empty strings.  In Meteor's templates, the entire template doesn't render :-P
 

[David Glasser]

This is worth filing as a bug on GitHub!

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[Daniel Dornhardt]

Hello,

i created a ticket: https://github.com/meteor/meteor/issues/801 - I hope that's alright as it is.

Thanks!