alexyoung / node-burrito

Walk and transform the javascript AST with rice and beans on the side

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.

node.label()

Return the label of the present node or null if there is no label.

Labels are returned for "call", "var", "defun", and "function" nodes.

Returns an array for "var" nodes since var statements can contain multiple labels in assignment.

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.