deferredTemplateLiterals.ts

/**
 * This approach has many limitations:
 *   - it does not accept variable names with numbers or other symbols (relatively easy to fix)
 *   - it does not accept arbitrary expressions (quite difficult to fix)
 */
function deferredTemplateLiteral(template: string, env: { [key: string]: string | undefined }): string {
  const varsMatcher = /\${([a-zA-Z_]+)}/
  const globalVarsmatcher = /\${[a-zA-Z_]+}/g

  const varMatches: string[] = template.match(globalVarsmatcher) ?? []
  const templateVarNames = varMatches.map(v => v.match(varsMatcher)?.[1] ?? '')
  const templateValues: (string | undefined)[] = templateVarNames.map(v => env[v])

  const templateInterpolator = new Function(...[...templateVarNames, `return \`${template}\`;`])

  return templateInterpolator(...templateValues)
}

// Usage:
deferredTemplateLiteral("hello ${thing}", {thing: "world"}) === "hello world"