Accessing handlebars variable via javascript

Question

I'm generating a handlebars view for express js framework, and I need to access the variables I pass to the view from inside a separate JavaScript file.

For example:

var foo = {{user.name}}

Someone got an idea? Helper?

Solution 1

The value of user.name needs to be output as a valid JavaScript expression if you want to include it in within a <script>, which will be reevaluating it as code.

Currently, if user.name is "john.doe" for example, the resulting script will be:

var foo = john.doe; // `john` is treated as an object with a `doe` property

---

The user.name at least needs to be in quotes so it's understood as a string value/literal.

var foo = "{{user.name}}";

// result
var foo = "john.doe";

You can also take advantage of JSON and JavaScript's similarities in syntax, outputting JSON that JavaScript can understand as an Expression, and will already include the quotes.

Handlebars.registerHelper('json', function (content) {
    return JSON.stringify(content);
});

var foo = {{{json user.name}}};

// result
var foo = "john.doe";

---

Note the triple {{{...}}} in the last example to disable HTML encoding, so you don't end up with:

var foo = "john.doe"

Solution 2

Node can pass encoded JSON to the handlebars-view like this:

result.render('index', { 
  encodedJson : encodeURIComponent(JSON.stringify(jsonData))
});

The handlebars-view can decode and parse the json like so:

<script>
  var decodedJson = decodeURIComponent("{{{encodedJson}}}");
  var jsonObj = JSON.parse(decodedJson);
</script>

---

Since anything passed to a handlebars-view will basically be injected straight into HTML, you should always pass encoded json and let the view decode it.

---

I tried the other suggestions in this thread. But they injected unencoded JSON into the handlebars view and that always gave me parsing errors. I have no idea how people got that to work, since it seems like Handlebars will parse variables as plain text.

I have not read up on how the Handlebars parser works - but it seems to me the only safe option is to use encoded JSON, like how I suggest in my examples.

Solution 3

I didn't know how to do this in a separate js file either. These answers led me in the right direction, so thank you! I ended up JSON stringifying the data on the server-side, before I passed it to the page via render. However, I still couldn't get the code to work in a separate js file - which is fine. My use case was for Materialize input form autocomplete.

node.js

// code is inside of a router.get block, therefore access to the response(res)

let customerData = {}
// add customer data with a loop, or whatever

const customers = JSON.stringify(customerData)

res.render('path/to/page', {
    customers
})

client-side js

// code placed within script tags of the handlebars file, not a separate js file

const customers = {{{customers}}}