spread.js is a small command line program that combines Node.js, Emacs and emacsclient into a minimalist's worksheet interface

spread.js evaluates the entire file with node. For each top-level expression, spread.js looks for a //-> marker. If it finds one, it inserts the result of that expression after the maker in the source file itself, replacing the previous value. Then it notifies Emacs via emacsclient to revert the buffer visiting the file.

This means that the result value of each top-level expression will appear in place, on the screen, in real time, just like they would in a spreadsheet or a worksheet interface.

The data is inserted into the source file in JSON syntax in such a way that the file continues to evaluates normally with Node.js.

If the following content is in foo.js

1 + 5                           //-> 0

"asd" + "qwe"                   //-> 0

var obj = { x: 10 }
obj.y = [1, 2, 3, { a:4, b: 2} ]
obj  //-> 0

var x = 5      //-> 0

After running spread.js foo.js the new content of the file will be

1 + 5                           //-> 6

"foo" + "bar"                   //-> "foobar"

var obj = { x: 10 }
obj.y = [1, 2, 3, { a:4, b: 2} ]
obj  //->
       0, {
            "x": 10,
            "y": [
              1,
              2,
              3,
              {
                "a": 4,
                "b": 2
              }
            ]
          }

var x = 5      //-> {}

and the corresponding Emacs buffer is updated.

Four things to note:

• A JSON values must appear to the right of the //-> maker. When writing an empty cell the first time, write //-> 0 or some other placeholder value.

• Single line JSON values are placed inside the marker comment; multiple line values are placed on the line below, indented. Since most top-level JSON values are valid javascript they do not interfere with the evaluation of the file

• However, since top-level object literals are not allowed on the top-level in Javascript, when outputing multi-line object literals spread,js prefixes them with a 0, to promote them to an expression. This maintains compatibility with normal evaluation with node.

• Since undefined is not a valid JSON value, undefined is output as as the empty object instead, {}.

Suggestions

In Javascript mode, bind C-c > to inserting a marker:

(define-key js-mode-map
  "\C-c>"
  (lambda () (interactive)
    (progn
      (end-of-line)
      (insert " //-> 0 "))))

Then configure Emacs to run spread.js on the after-save-hook for every files that ends in .spread.js

(add-hook
 'after-save-hook
 (lambda ()
   (when (string-match
          "[.]spread[.]js$"
          (buffer-file-name))
     (shell-command (concat "spread.js " (buffer-file-name) " &")))))

Known Bug

• Any text to the right of the value but inside of the marker comment will be evaluated.