obj.hasOwnProperty undefined is not a function nodejs

[fotisp]

Hello,

I was noticing some discrepancies in some of the rendering of the nunjuck templates. After enough digging around I boiled it down to different nodejs versions between development and production. However the production machine has a more resent version of nodejs.

~ > node --version
v0.12.2

With version v0.12.x of node, this line

https://github.com/mozilla/nunjucks/blob/master/src/lib.js#L271

fails with TypeError: undefined is not a function.

Has anyone encountered this, is there any know workaround?

[fotisp]

Sorry,

An example that causes problems is

        {% for key,value in extra  %}
          <input type="hidden" name="{{ key  }}" value="{{ value }}" />
        {% endfor %}

Where extra is just a JSON object.

[waynebloss]

@fotisp What do you mean that extra is a JSON object?

I tried the following in node 0.12 and it works fine:

var extra = require('./extra.json');
console.log(extra.hasOwnProperty('key'));

and the output is true.

This also shows that extra has a working hasOwnProperty method:

var extra = JSON.parse('{"key": "val"}');
console.log(extra.hasOwnProperty('key'));

[devoidfury]

Does the JSON object you've got have a property hasOwnProperty? That's the only way I could reproduce that error, TypeError: undefined is not a function.

extra = { hasOwnProperty: undefined }

Could you provide a full test case that produces the error?

[devoidfury]

This could also happen if the object does not have Object in it's prototype chain, for example:

extra = Object.create(null)

The safer way to handle this case would be to change https://github.com/mozilla/nunjucks/blob/master/src/lib.js#L271 to this:

 if(Object.prototype.hasOwnProperty.call(obj, k)) {

--- the only issue with that is that it may break some older browser compatibility, so we'd need to add extra logic for that.

[jlongster]

@fotisp, can you check out @devoidfury's comments above?

[fotisp]

Hi @jlongster,

I will try to take a look during the weekend and report back.

[xtr0]

This could also happen if the object does not have Object in it's prototype chain, for example:

extra = Object.create(null)

Please note: For example in express.js res.locals is created in exactly this way intentionally. So if one is using res.locals in renderString as a context there is an issue with migration to nunjucks 2+ (yeah, it is possible to replace res.locals with something like _.extend({}, res.locals), but...)

(and sorry for my English)

[carljm]

I'm not convinced this is worth fixing, but if someone wanted to look into the browser-compatibility implications of the Object.prototype.hasOwnProperty.call(...) solution suggested above, I'd consider it.

[asprouse]

@carljm This is enough of a problem that ESLint has a rule about it. http://eslint.org/docs/rules/no-prototype-builtins This setting was enabled in v4 of Airbnb's widely (43k+ stars) used ESLint config. I have noticed some libraries, notably graphql-js, creating objects with Object.create(null);passing them into nunjucks throws this error.