Check if page.data.x is defined

[gibfahn]

Is there a way to check whether a variable is defined?

I've tried some suggestions from Shopify/liquid#89 and Shopify/liquid#223, and haven't found something that works.

Trying something like:

{% if page.data.nav  %}
## Foo
{% endif %}

results in

Error: Failed to render content for "index.html"
Caused by: Rendering error: Invalid index `nav` for value 
`Object({"heading": Str("Gibson Fahnestock")})`

[epage]

Check my post on #363

[epage]

Quick summary:

{% if page contains "title" %}
{% endif%}

and I plan to add back in {% if page.data.nav %} support in the future.

[gibfahn]

I tried that but couldn't get it to work:

{% if page.data contains nav  %}
## Foo
{% endif %}

Error: Failed to render content for "index.html"
Caused by: Rendering error: Object key not found: "nav"

EDIT: I didn't read what you wrote properly, sorry! If you quote the nav then it works.

[epage]

So you've got it working now?

[gibfahn]

So you've got it working now?

Yes, got it working.

Not sure how you do it for a top-level variable though (equivalent of {% if nav %}), is that currently possible?

[epage]

Not sure how you do it for a top-level variable though (equivalent of {% if nav %}), is that currently possible?

At the moment, you can't. I plan to add back in support for this.

The problem is previously, it treated any non-existent variable name as if it was nil. When migrating across a major breaking change in cobalt, I wanted people people to know when they were accessing the old name of a variable, so I made them all errors.

As time passes and I'm more confident people have migrated, I'll be adding a special case to the if tag so that if its just a variable name, it will return false if it does't exist.