I have this code:

_.templateSettings = {interpolate : /\{\{(.+?)\}\}/g};

var _d = _.template($('#_d').html());

$.get('/foo', function(data) {
    $('#output').html(_d(data));
});

and in HTML:

<div id="_d">
    {{name}} {{phone}}
</div>
<div id="output"></div>

/foo returns something like {"name":"joe","phone":"12345"}, but sometimes it doesn't have phone thus simply returns {"name":"joe"}, which will choke template evaluation thus nothing gets printed in output. How do I make a variable optional?

EDIT: /foo is beyond my control

I have this code:

_.templateSettings = {interpolate : /\{\{(.+?)\}\}/g};

var _d = _.template($('#_d').html());

$.get('/foo', function(data) {
    $('#output').html(_d(data));
});

and in HTML:

<div id="_d">
    {{name}} {{phone}}
</div>
<div id="output"></div>

/foo returns something like {"name":"joe","phone":"12345"}, but sometimes it doesn't have phone thus simply returns {"name":"joe"}, which will choke template evaluation thus nothing gets printed in output. How do I make a variable optional?

EDIT: /foo is beyond my control

• javascript
• templates
• underscore.js

6 Answers 6

The || operator is useful for this sort of thing:

$.get('/foo', function(data) {
    data.phone = data.phone || "";
    $('#output').html(_d(data));
});

But since you're already using Underscore, you can use the _.defaults function. This approach is particularly useful for providing defaults for multiple fields:

$.get('/foo', function(data) {
    _.defaults(data, {name : 'joe', phone : ''});
    $('#output').html(_d(data));
});

I liked @namuol solution, another thing that we could do is set the defaults hash at the model extends

var MyModel = Backbone.Model.extend({
    defaults: {
        "foo": "I",
        "bar": "love",
        "yeah": "sara"
    }
});

Just another option.

You can have an html

<div id="d">
    {{data.name}} {{data.phone}}
</div>

Use the template as below to avoid undefined variable issue for phone

_.templateSettings = {
  interpolate : /\{\{(.+?)\}\}/g
};

var template = _.template($('#d').html());
var jsonResponse = {"name":"Jeo"}; // phone is missing
var result = template({"data":jsonResponse});

A practical solution would be to include phone in the object, but with an empty value:

{"name":"joe","phone":""}

There are some good answers above, but you can use _.partial to get a single function that applies a template with defaults:

foobarTemplate = _.template('<%=foo%><%=bar%>')
barPrefilled = _.partial(_.defaults, _, {bar:'def'})
foobarTemplate(barPrefilled({foo:'abc'}))
//  "abcdef"
foobarTemplateWithDefaults = function (data) {return foobarTemplate(barPrefilled(data));}
foobarTemplateWithDefaults({foo:'wat'})
//  "watdef"
foobarTemplateWithDefaults({foo:'foo', bar:'bar'})
//  "foobar"

And then there is the obvious: Put this in the top of your template:

<%
  if (typeof(phone) === "undefined") {
    phone = "";
  }
%>

Working snippet:

$(function() {
  $('#result').html(
    _.template(
      $('#template').html(), {
        interpolate: /\{\{(.+?)\}\}/g
      }
    )({
      foo: 23,
      // No value for bar
      // bar: 11,
    },)
  )
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script type="x-template" id="template">
<%
  if (typeof(bar) === "undefined") {
    bar = "default";
  }
%>
This is {{ foo }} and {{ bar }}
</script>

<div id="result"></div>

(also as jsfiddle)