parse body of a function given constraints

parse-function-body.js

// 24 June 2022
// parse the body of a function if its only parameter is self

// 25 june 2022
// - added full body test,
// - fixed trailing brace regexp (missing $).

// 29 June 2022
// - append semi-colon and linebreak to each parsed function body, to enable
//   concatenating multiple functions in the next post, "communicating embedded
//   worker factories" at
//   https://gist.github.com/dfkaye/c6d77fde86aea70ef6ae79bda2219582

// ...companion to "parse parameter names from function argument list"
// at https://gist.github.com/dfkaye/51550ec0818e507aebd89a585b2c05c4

// ...continued from "import an embedded worker within another embedded worker"
// at https://gist.github.com/dfkaye/20ff0934cd8d2b0fa7aea5606ac7ab89

// Self() is a special purpose function meant to extract a stringified function
// body for use as an embedded worker script, loaded as a blob with an object
// URL.

// Self() extracts the body of a function argument if:
// 1. it has only one argument,
// 2. the argument is `self` or has a `self` property defined (i.e., `self` is
//    not a fallback, as in `( self = "value" )`, e.g.),
// 3. it's an arrow function, and
//   3.1 parentheses surround the function argument,
//   3.2 braces surround the function body.

// Self() is meant to extract a stringified function body for use as an embedded
// worker script, loaded as a blob with an object URL.

function Self(fn) {
  var fs = String(fn).trim();

  var parseable = typeof fn == "function"
    && fn.length === 1
    && fs.match(/(self)[^\)]*\)[^\{]*\{/);

  if (!parseable) {
    return;
  }

  return fs /* .substring(fs.indexOf("self") + 4) */
    .replace(/(self)?[^\)]*\)[^\{]*\{/, '')
    .replace(/\s*\}\s*$/, '')
    .split("\n")
    .filter(s => /\S/.test(s))
    .join("\n")
    .concat(";\n");
}

/* test it out */

console.group("* failing *");
  [
    function Named (param) { console.log( "named" ); },
    function (param) { console.log( "anonymous" ); },

    function Named ( { param = "function" }) { console.log( "named:param" ); },
    function ( { param = "function" }) { console.log( "anonymous:param" ); },

    param  =>  "arrow",
    ( { param = "arrow"} )  => "arrow:param",
    ( { param = "arrow"} )  => { "arrow:braces" },

    self  =>  "arrow:no-braces",
    self  => { "arrow:braces:no-parens" },
    ( self = "arrow" ) => { "arrow:parens:fallback" }
  ].forEach(fn => {
    console.log(Self(fn))
  });
console.groupEnd("* failing *");

console.group("** passing **");
[
  function (self) { console.log( "anonymous:self" ); },
  function Named (self) { console.log( "named:self" ); },
  ( self ) => {
   console.log( "arrow:self" );
  },

  function Named ( { self = "function" } ) { console.log( "named:self:param" ); },
  function ( { self = "function" } ) { console.log( "anonymous:self:param" ); },
  ( { self = "arrow" } )  => {
    console.log("arrow:self:param");
  }
].forEach(fn => {
  console.log(Self(fn))
});
console.groupEnd("** passing **");

console.group("*** fullbody ***");

function FullBody(self) {
  
  // full body script test
  
  function credentials({ sender, address }) {
    return address === self.location
      && senders.has(sender)
  }

  self.senders = new Set();

  self.init = function(data) {
    senders.has(data.sender) || senders.add(data.sender);

    return credentials(data);
  }

  self.onmessage = function (request) {
    var data = Object(request.data);

    console.warn(data.sender, data.address, data.action, data.value);

    if (data.action === 'init') {
      self.init(data);
    }

    var response = Object.assign({}, data);
    
    self.postMessage(response);
  }

  
}

console.log(
 Self( FullBody )
);

console.groupEnd("*** fullbody ***");

/*
* failing *
undefined
undefined
undefined
undefined
undefined
undefined
undefined
undefined
undefined
undefined
** passing **
 console.log( "anonymous:self" ); debugger eval code:83:11
 console.log( "named:self" ); debugger eval code:83:11
   console.log( "arrow:self" ); debugger eval code:83:11
 console.log( "named:self:param" ); debugger eval code:83:11
 console.log( "anonymous:self:param" ); debugger eval code:83:11
    console.log("arrow:self:param");
*** full body ***
  // full body script test
  function credentials({ sender, address }) {
    return address === self.location
      && senders.has(sender)
  }
  self.senders = new Set();
  self.init = function(data) {
    senders.has(data.sender) || senders.add(data.sender);
    return credentials(data);
  }
  self.onmessage = function (request) {
    var data = Object(request.data);
    console.warn(data.sender, data.address, data.action, data.value);
    if (data.action === 'init') {
      self.init(data);
    }
    var response = Object.assign({}, data);
    self.postMessage(response);
  }
*/