freethenation / node-falafel

transform the ast on a recursive walk

free-falafel

Transform the ast on a recursive walk.

This module is like burrito, except that it uses esprima instead of uglify for friendlier-looking ast nodes.

Example

array.js

Put a function wrapper around all array literals.

var falafel = require('free-falafel');

var src = '(' + function () {
    var xs = [ 1, 2, [ 3, 4 ] ];
    var ys = [ 5, 6 ];
    console.dir([ xs, ys ]);
} + ')()';

var output = falafel(src, function (node) {
    if (node.type === 'ArrayExpression') {
        node.update('fn(' + node.source() + ')');
    }
});
console.log(output);

output:

(function () {
    var xs = fn([ 1, 2, fn([ 3, 4 ]) ]);
    var ys = fn([ 5, 6 ]);
    console.dir(fn([ xs, ys ]));
})()

Methods

var falafel = require('free-falafel')

falafel(src, opts={}, fn, breadthFirstFn)

Transform the string source src with the function fn, returning a string-like transformed output object.

For every node in the ast, fn(node) fires. The recursive walk is depth first, so children get called before their parents.

Performing the transforms during a depth first traversal makes it easier to write nested transforms since transforming parents often requires transforming all its children first.

The return value is string-like (it defines .toString() and .inspect()) so that you can call node.update() asynchronously after the function has returned and still capture the output.

Instead of passing a src you can also pass opts.source or, if the source code has already been parsed into an ast, you can pass opts.ast.

All of the opts will be passed directly to esprima except for 'range' which is always turned on because falafel needs it.

Some of the options you might want from esprima includes: 'loc', 'raw', 'comments', 'tokens', and 'tolerant'.

You can optionally provide the function breadthFirstFn. This function will be called before fn during a breadth first traversal of the ast. This function allows you to add additional properties to the node parameter so that you can easily do things like not transforming any code inside of a function definition. There is an example of this below.

Nodes

Aside from the regular esprima data, you can also call some inserted methods on nodes.

Aside from updating the current node, you can also reach into sub-nodes to call update functions on children from parent nodes.

node.source()

Return the source for the given node, including any modifications made to children nodes.

node.update(s)

Transform the source for the present node to the string s. This function is not available during the breadth first traversal of the ast.

Note that in 'ForStatement' node types, there is an existing subnode called update. For those nodes all the properties are copied over onto the node.update() function.

node.parent

Reference to the parent element or null at the root element.

More Examples

breadthFirstFn example

Put a function wrapper around all array literals that are not inside of a function definition.

var falafel = require('free-falafel');

var src = '(' + function () {
    var xs = [ 1, 2, [ 3, 4 ] ];
    var ys = [ 5, 6 ];
    somefunc([ xs, ys ]);
} + ')();\n';
src += 'var g = [ 5, 6 ];';

var output = falafel(src, 
    function (node) {
        if (node.type === 'ArrayExpression' && !node.inFunc) {
            node.update('fn(' + node.source() + ')');
        }
    },
    function (node) {
        if (node.type === 'FunctionExpression') {
            node.inFunc = true;
        }
        else if (node.parent && node.parent.inFunc) {
            //inherit from parent
            node.inFunc = node.parent.inFunc;
        }
        else { node.inFunc = false; }
    });
console.log(output.toString());

output:

(function () {
    var xs = [ 1, 2, [ 3, 4 ] ];
    var ys = [ 5, 6 ];
    somefunc([ xs, ys ]);
})();
var g = fn([ 5, 6 ]);

You can play with this example at JS Bin here

Install

With npm do:

npm install free-falafel

License

MIT