resumable-eval

Resumable eval is a microlibrary (<20 LOC) for pausing and resuming eval. This lets you properly capture of scope of functions in code and interact with those scopes on an as-needed basis.

For example,

var resumable = require('resumable-eval')

var session

;(function() {
  var x = 1
  session = eval(resumable)
})()

session
  .eval('x')
  .result // returns 1

session
  .eval('var y = 3')
  .eval('x + y')
  .result // returns 4

Note that trying to do this in the naive way fails:

var naiveEval

;(function() {
  var x = 1
  naiveEval = function(code) { return eval(code) }
})()

naiveEval('x') // This returns 1 but ...

naiveEval('var y = 3')
naiveEval('x + y') // This fails because y is undefined

This is why we need resumable-eval :)

Why this can be useful

Most languages have REPLs, which give you resumable eval in the global scope. What if you could have a REPL in function scope, without a breakpoint? resumable-eval is a utility that gives you that ability.

Lazy sessions

You might want to capture the scope of many functions. Maybe all of your functions. But you might not want to call eval everywhere. In that case, you can implement a lazy pattern:

var lazySession

;(function() {
  var x = 1
  lazySession = function() {
    return eval(resumable)
  }
})()

Now when we want to use the eval session,

var session = lazySession()
session.eval('x')

In this way we can capture the scopes of many functions but only create sessions on an as-needed basis.

Tests

To run the tests, clone the repo and install nodeunit:

git clone https://github.com/omphalos/resumable-eval
cd resumable-eval
npm install -g nodeunit

Then:

npm test

License

MIT