burrito

Burrito makes it easy to do crazy stuff with the javascript AST.

This is super useful if you want to roll your own stack traces or build a code coverage tool.

examples

microwave

examples/microwave.js

var burrito = require('burrito');

var res = burrito.microwave('Math.sin(2)', function (node) {
    if (node.name === 'num') node.wrap('Math.PI / %s');
});

console.log(res); // sin(pi / 2) == 1

output:

1

wrap

examples/wrap.js

var burrito = require('burrito');

var src = burrito('f() && g(h())\nfoo()', function (node) {
    if (node.name === 'call') node.wrap('qqq(%s)');
});

console.log(src);

output:

qqq(f()) && qqq(g(qqq(h())));

qqq(foo());

methods

var burrito = require('burrito');

burrito(code, cb)

Given some source code and a function trace, walk the ast by expression.

The cb gets called with a node object described below.

burrito.microwave(code, context={}, cb)

Like burrito() except the result is run using vm.runInNewContext(res, context).

node object

node.name

Name is a string that contains the type of the expression as named by uglify.

node.wrap(s)

Wrap the current expression in s.

If s is a string, "%s" will be replaced with the stringified current expression.

If s is a function, it is called with the stringified current expression and should return a new stringified expression.

If the node.name === "binary", you get the subterms "%a" and "%b" to play with too. These subterms are applied if s is a function too: s(expr, a, b).

Protip: to insert multiple statements you can use javascript's lesser-known block syntax that it gets from C:

if (node.name === 'stat') node.wrap('{ foo(); %s }')

node.node

raw ast data generated by uglify

node.value

node.node.slice(1) to skip the annotations

node.start

The start location of the expression, like this:

{ type: 'name',
  value: 'b',
  line: 0,
  col: 3,
  pos: 3,
  nlb: false,
  comments_before: [] }

node.end

The end location of the expression, formatted the same as node.start.

node.state

The state of the traversal using traverse.

node.source()

Returns a stringified version of the expression.

node.parent()

Returns the parent node or null if the node is the root element.

installation

With npm you can just:

npm install burrito

kudos

Heavily inspired by (and previously mostly lifted outright from) isaacs's nifty tmp/instrument.js thingy from uglify-js.