How do I template a Javascript file with Ansible?

I want to create an Ansible role to install and configure Node-RED and I'm struggling with templating the settings.j2 file.

- name: Write the NodeRED settings file
  ansible.builtin.template:
    src: templates/settings.js.j2
    dest: "{{ _nodered_user_info.home }}/.config/node-red/settings.js"
    mode: "0644"
    owner: "{{ _nodered_user_info.name }}"
    group: "{{ _nodered_user_info.name }}"
  become: true

settings.js.j2

This always throws the error:

The error was: . expected token 'end of print statement', got 'string'

I assume that Jinja2 is having difficulties with the single curly braces in the JavaScript file.

The syntax highlighting is not highlighting the first if tag properly.

I tried to replace all {with {{ '{' }} and all } with {{ '}' }}, but this makes the file unreadable and breaks the syntax highlighting.

Solution

When your template source file is supposed to contain a lot of characters conflicting with the default jinja2 delimiters, you can change those directly in the template module. So for example:

- name: Template my js file
  ansible.builtin.template:
    src: my.js.j2
    dest: path/to/dest.js
    block_start_string: '<@'
    block_end_string: '@>'
    comment_start_string: '<#'
    comment_end_string: '#>'
    variable_start_string: '<:'
    variable_end_string: ':>'

should let you process a template looking like the following. Of course change the above (and below) to whatever best suits your needs:

<# This is a jinja template with custom delimiters #>
{
  "toto": "<: my_variable :>",
  "titi": {
  <@ if some_titi_switch @>
    "some_key": "a static value"
  <@ else @>
    "other_key": "some other value"
  <@ endif @>
}