Convert JS interpolation string to function call

Question

I'm writing some code that rips string literals out of Typescript/JavaScript source as the first stage of a localisation toolchain I have planned.

The fly in the ointment is string interpolation.

I was on the verge of writing a function to transform an interpolation string into a function call that rips the expressions and then replaces the interpolation string with a function call that takes the expressions as parameters.

const a = 5;
const b = 7;
const foo = `first value is ${a + b}, second value is ${a * b}`;

becomes

import { interpolate } from "./my-support-code";
...
const a = 5;
const b = 7;
const foo = interpolate("first value is ${0}, second value is ${1}", [a + b, a * b]);

with the interpolate function working through the array values and replacing strings generated from the ordinal position

function interpolate(template: string, expressions: Array<any>): string {
  for (let i = 0; i < expressions.length; i++) {
    template = template.replace("${" + i + "}", expressions[i].toString());
  }
  return template;
}

This will probably work (not yet tried) but it occurred to me that this is probably a thoroughly invented wheel. The question is basically is there a well-established package that does a comprehensive job of this?

I know the above doesn't localise anything. The point is to be rid of interpolation strings so the substitution mechanism can assume that all strings are simple literals. The base language string taken from the above would be "first value is ${0}, second value is ${1}" and translators would be expected to place the tokens appropriately in whatever string they produce.

Answer 1

If you're going to tackle this on a non-trivial sized code base, the best you can really do is:

1. Write a regular expression to identify common types of localization targets and identify them, probably by file + line number.
2. Add comments to your code in these locations using a keyword that's easy to git grep for, or even something that can be added to your editor's syntax highlighting rules. Personally I use things like // LOCALIZE.
3. If you're feeling ambitious, you could implement a rewriter that attempts to convert from template form to your localization's template requirements. Each conversion can be individually inspected, altered as required, and introduced. Hopefully you have test coverage to verify your code still works after this.