Nunjucks: String interpolation options

[valtido]

I was wondering if there is already a solution in place for string interpolation.

If not can we put the following filter as a default nunjucks one? instead of adding it manually for each project?

I have the following template:

{# /index.html #}

<div>
   {{ message | interpolate }}
</div>

where ctx.message = "Hello {{ there }}";
and where ctx.there = "world!!!"

and I have added the following filter:

env.addFilter('interpolate', function(str) {
    return nunjucks.renderString(str, this.ctx)
})

output is: <div>Hello world!!!</div> not <div>Hello {{ there }}</div>

[revelt]

I haven't found a way to do that either. When I need string interpolation I use set to create a new variable from multiple pieces: strings and other variables. It's tedious but it works.

If only we could use ES6 String literals within Nunjucks...

[ArmorDarks]

What exactly you want to do?

Do you want to force rendering of a string, like this?

{% set tmpl = 'Hi {{ name }}' %}

{{ tmpl }}

And to make tmpl output Hi Nick, not Hi {{ name }}, right?

[valtido]

Yes exactly that. 👍

[fdintino]

If you want to pass a nunjucks template string to a template and do a nested render then I think you are best off writing your own filter for that, because it seems like a rather niche case. But if you don't need to pass the template fragment into context you can use the {% set %} / {% endset %} tags:

var tmpl = `
{% set greeting %}Hello {{ name }}{% endset %}
{{ greeting }}
`;

nunjucks.renderString(tmpl, {'name': 'Nick'}); // outputs "Hello Nick"

[valtido]

I kindly disagree string interpolation is not a niche case should be a standard but let's agree to disagree :)

[ArmorDarks]

I support @fdintino, after using Nunjucks for years I can say that it is indeed quite a specific need.

Anyway, as far as I know, Jinja2 does not provide a built-in filter to do such thing.

Considering that, I recommend @valtido to open issue about such filter in Jinja2 repository. If it will be accepted there, surely it will appear in Nunjucks.

[fdintino]

I think there might be some confusion. What was provided in the first example is not string interpolation but a nested render. That can generally be accomplished with a {% set %}{% endset %} block in most cases. Jinja2 has the | format filter (which uses python/printf string formatting), I think it would be logical to similarly support es6 template literals. But a filter that calls nunjucks.renderString is problematic. Does it use the calling nunjucks environment or a fresh environment? How do you pass options? Does it use a loader? Those questions make it difficult to write a general-purpose render filter.

[equinusocio]

Still missing this basic feature. Any update?

[khera-shanu]

People who think string interpolation is a niche case, they should code more often!

[valtido]

I think there might be some confusion. What was provided in the first example is not string interpolation but a nested render. That can generally be accomplished with a {% set %}{% endset %} block in most cases. Jinja2 has the | format filter (which uses python/printf string formatting), I think it would be logical to similarly support es6 template literals. But a filter that calls nunjucks.renderString is problematic. Does it use the calling nunjucks environment or a fresh environment? How do you pass options? Does it use a loader? Those questions make it difficult to write a general-purpose render filter.

I think you spot on with that, es6 flavoured, I think at the time of raising this issue, I was confined with my line of thought as I was also a noob. however, to help a developer save precious time, you should implement es6 flavoured strings. Best of luck.

[winston0410]

Same here. Any update on this?

[benseven]

Same here.

[sippeangelo]

This "niche case" is literally the first thing I ran into

{{ `Changelog for ${project.name}` | center }}

Template render error: (unknown path) [Line 1, Column 15]
  expected variable end

[sippeangelo]

Here's a neat little hack for a Jinja-like "format" filter using ES6 string templating, if you're feeling brave:

env.addFilter('format', str => {
    return (new Function('with (this) { return `' + str + '` }')).call(context)
})

This will let you do things like

{{ 'Changelog for ${project.name}' | format | center }}