Allow for transforms

[raijinsetsu]

Great library!

I am using it to generate log output according to the installation's configuration. We deploy to various environments and how they parse/understand the log entries differs.

Here is what we are doing:

const template = parse({
    severity: '{{ucLogLevel}}'
});

const result = template({
                logLevel: level,
                lcLogLevel: () => level.toLowerCase(),
                ucLogLevel: () => level.toUpperCase(),
            })

The issue is that the actual template is provided by configuration and we need to provide each of the variables in a bunch of possible styles: strings in uppercase, lowercase, and, possibly, title case; numbers might need rounding; dates might need manipulation (ie. as a unix timestamp vs. ISO 8601 timestamp vs. Windows timestamp, etc.).

I would NOT suggest allowing code to be embedded inside the template as that would pose a security risk unless you added a lot of complexity (ie. using a library to sanitize the code so that only a subset of features could be used).

However, the parse function COULD accept a list of transforms.

I would propose the following, given by example:

const template = parse({
    severity: '{{logLevel:default->toUpperCase}}'
},{
    string: {
        toUpperCase: (val) => val.toUpperCase(),
        toLowerCase: (val) => val.toLowerCase()
    },
    number: {
       round: (val) => Math.round(val)
    }
});
// template.keys => typical stuff
// template.transforms => the second parameter passed to parse

const result = template({logLevel: level})

If a PR were submitted for this, would it be accepted?

[curran]

Yes! PRs warmly welcome, as long as they are backwards compatible and have tests & documentation in them.

Looks like a neat feature to add.

[raijinsetsu]

Would you have issues if I pull in the typings, from @types/json-templates? It would mean that this package's maintainers would have to take-over the maintenance of those definitions. I know several other projects have done this to make it easier to keep the definitions in sink with the library.

[curran]

I would rather the types live externally, please. I have zero interest in maintaining types for this. Thanks!