Quick and dirty interpolation method (outermost pairs only)

interpolate.js

// Example Usage
var str = "Result: {foo({bar: true})} other stuff"
var result = interpolate(str,'{', '}', handle_chunk)

console.log(result.join('')) // outputs: Result: success!  other stuff

function handle_chunk(chunk) {
  var fn = new Function('foo', 'return ' + chunk)
  return fn(foo)
}

function foo(data) {
  if (data.bar === true) return "success! "
  else return "failed :("
}

function interpolate(str, begin_token, end_token, callback) {
  // should probably sanitize this input, javascript needs a RegExp.escape method :/
  var regexp = new RegExp(begin_token +'|' + end_token, "gm")
    , token
    , open = 0
    , begin = 0
    , chunks = []
  console.log('str: ', str)
  while((token = regexp.exec(str))) {
    if (token[0] === begin_token) {
      // if we're opening a new interpolated chunk, flush all the previous text to the chunks array
      if (open === 0) {
        chunks.push(str.substr(begin, token.index - begin))
        console.log('text chunk: ', JSON.stringify(chunks[chunks.length - 1]))
        begin = token.index + 1
      }
      open += 1
    } else if (token[0] === end_token && open > 0) { // only handle closing outermost pairs
      open -= 1
      // if we've found the end of an interpolated chunk send it to the callback
      if (open === 0) {
        chunks.push(callback(str.substr(begin, token.index - begin), begin, token.index - begin))
        console.log('interpolated chunk: ', JSON.stringify(chunks[chunks.length - 1]))
        begin = token.index + 1
      }
    }
  }
  chunks.push(str.substr(begin))
  return chunks
}