urlTemplateInterpolation.js

// this could definitely be moved out to a helper/util.
// I'd consider this a better and less fallible approach to our previous ideas of using {{token}}.
const defaultValue = '';

// see MDN reference on TaggedTemplates for how the strings&keys work.
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals
const urlTemplate = (strings, ...keys) =>
  // returns a function that accepts a property bag (presumably to fill in the tokens)
  (props) =>
    // start with the first string, then map each tokenized Key to a tuple of: `Properties[Key], NextString`
    // now you have [string0] + [ [value, string1], [value, string2], ... ].flat() and you slap it all together with .join
    [strings[0]].concat(
      keys.map((k, i) => [
        (props[k] || defaultValue),
        strings[i+1]
      ]).flat()
    ).join('');

// say you want to templatize a url
// the interspersed ${string} become tokens in the template
// that way, we can replaced those tokens with values from an object
// this guarantees that parsing the string as tokens succeeds
//   (eg: doing `foo/{{bar}}/baz` runs the risk of needing {{}} characters and having to escape, however small.)
const template = urlTemplate`/engage/tool/${'toolName'}?patientId=${'patientId'}&encounterId=${'encounterId'}`
// etc. Yes, I know that `${'xyz'}` looks funny. pls see references


// later on in your existing code we should use the standard set of session/context properties to send to the urlreplacer function
const context = { encounterId: activeEncounterId, patientId, userId: activeUserId };

const resultingUrl = template(context);