comma.md

{{,}}

Produces a literal comma (,) exactly if it is required for valid JSON.

Usage

If conditional expressions follow each other, it can be hard to say whether a comma is needed or not to obtain valid JSON:

<template>
{
  {{if maybe }}   "foo": "bar" {{end}} {{// place a comma here? }}
  {{if perhaps }} "bar": "baz" {{end}} {{// or here? }}
  {{: may-be-empty }}
}
</template>

If the first condition is true, a name/value pair will be produced. If and only if the second condition is true as well, a comma will be needed to separate both pairs. The same applies to the following pair producer {{: …}} which may yield nothing.

To avoid having to repeat various combinations of the conditions to decide whether or not to emit a comma, use the comma command {{,}} to automatically produce all required commas:

<template>
{
  {{if maybe }}   "foo": "bar" {{end}} {{,}}
  {{if perhaps }} "bar": "baz" {{end}} {{,}}
  {{: may-be-empty }}
}
</template>

The {{,}} could be placed in the body of {{if}} as well:

  {{if maybe }}   "foo": "bar" {{,}} {{end}}
  {{if perhaps }} "bar": "baz" {{,}} {{end}}

📎 Note that the comma may appear after some whitespace in the output string.

The use of the {{,}} should be seen as a last resort, because it impairs the template's readability. In many cases, the decision whether to place a comma or not can be made a priori by reordering the name/value pairs, producing leading commas in conditionals or having a fixed {{else}} block.

The {{loop}} command produces commas between its productions, too. In loop bodies comma commands are allowed but usually not necessary.