<%= and <%- output null

[colinta]

actually, in the version I was using in my project, <%= test %> outputs "" when {test:null}. but in the latest underscore, it outputs "null"

javascript
console.log(_('[<%= test %>] {<%- test %>}').template({test: null}));

outputs `[null] {null}`

This patch outputs `[] {}`.

[colinta]

I'm not a fan of the fix for interpolate (bfc7639), though it is simple and does pass the tests. But maybe there is a more elegant solution.

[colinta]

I've added a try..catch block to detect undefined variables. This brings it more into django-esque behavior.

In doing so, I also added similar support (for null and undefined) into _.escape, which may be undesirable. Please let me know, so I can fix my project code. I think the template language benefits from this feature, but that's me!

I did not create a minified version. I stick to uglifyjs, but that's not what you are using here (too much diff)

[octatone]

It seems like you are adding type/value tests to a function purposed for blindly escaping HTML characters. Would it not make more sense to check the variable type/value before passing it to the template in your own code?

I understand why you might want _.escape to do what you are asking, but I think it's outside the realm of what _.escape is meant for.

[colinta]

@octatone, Yeah, I agree about _.escape. As a core function, I don't like the idea of putting type checks in there.

Then again, I hate that '' + null === "null" and var a; '' + a === "undefined". I would much prefer these to be "". _sigh_.

I've moved the code for that into the _.template method. I hope that someone from documentcloud gets a chance to consider the relative value of having _.escape(null) === "", but until then, I'm still very happy if the following code works:

<form>
<table>
  <tr>
    <th>Name</th><th>Email</th>
  </tr>
</table>
<button id="add_another">+ Add Another</button>
</form>

<script type="text/html" id="user_form">
<tr>
  <td><input type="text" name="user-<%= index %>-name" value="<%- user.name %>" /></td>
  <td><input type="text" name="user-<%= index %>-email" value="<%- user.email %>" /></td>
</tr>
</script>

<script type="text/javascript">

  var data = [
        {name: 'Colin', email: 'colinta@gmail.com' }
      , {name: null, email: null }
      , {}
    ]
    , template = _chz.user_form;

  _(data).each(function(row, index) {
    $('table').append(template({user: row, index: index}));
  });

  $('#add_another').on('click', function() {
    var index = $('table tr').length - 1;

    $('table').append(_chz.user_form({user: {}, index: index }}));
    return false;
  });

</script>
```html

I would expect this to result in:

```html
<form>
<table>
  <tr>
    <th>Name</th><th>Email</th>
  </tr>
<tr>
  <td><input type="text" name="user-0-name" value="Colin" /></td>
  <td><input type="text" name="user-0-email" value="colinta@gmail.com" /></td>
</tr>
<tr>
  <td><input type="text" name="user-1-name" value="" /></td>
  <td><input type="text" name="user-1-email" value="" /></td>
</tr>
<tr>
  <td><input type="text" name="user-2-name" value="" /></td>
  <td><input type="text" name="user-2-email" value="" /></td>
</tr>
</table>
<button id="add_another">+ Add Another</button>
</form>

Right now, this code ends up with "null" and "undefined" strings all over the place. Coming from mustache, django and jinja, this was a surprise to me.

[braddunbar]

I think that the try...catch is a bit overkill, but I can definitely see the usefulness of printing '' instead of 'null' or 'undefined'. Also, it would be great to see a performance comparison.

[colinta]

I know. I cringed when I put that in there, but that was the only way I could come up with that allowed <%= a.b..c %>, where a is undefined.

I haven't done a thorough comparison, but a rough one - running the 'utility' tests, puts them neck and neck. I will post a thorough benchmark later today.

On Apr 18, 2012, at 7:13 AM, brad dunbarreply@reply.github.com wrote:

I think that the try...catch is a bit overkill, but I can definitely see the usefulness of printing '' instead of 'null' or 'undefined'. Also, it would be great to see a performance comparison.

---

Reply to this email directly or view it on GitHub:
#559 (comment)

[braddunbar]

I don't think that we should swallow errors like <%= a.b %> where a is undefined. It prevents getting a good stack trace, especially when the expression contains a function call as in <%= foo() %>.

[colinta]

It's your call. I would be happy with either of two solutions:

1. output nothing (coerce null/undefined to "")
2. raise an error

The only solution I am not happy with is when it outputs "null" or "undefined". To me, that is coercing to an incorrect string.

[jashkenas]

This is a duplicate of the earlier #556 -- so let's move the conversation over there. In any event, we aren't going to add a try/catch to our interpolations.