index.js

var parse = require('esprima').parse;
var objectKeys = Object.keys || function(obj) {
        var keys = [];
        for (var key in obj) keys.push(key);
        return keys;
    };
var forEach = function(xs, fn) {
    if (xs.forEach) return xs.forEach(fn);
    for (var i = 0; i < xs.length; i++) {
        fn.call(xs, xs[i], i, xs);
    }
};

var isArray = Array.isArray || function(xs) {
        return Object.prototype.toString.call(xs) === '[object Array]';
    };

module.exports = function(src, opts, fn) {
    if (typeof opts === 'function') {
        fn = opts;
        opts = {};
    }
    if (typeof src === 'object') {
        opts = src;
        src = opts.source;
        delete opts.source;
    }
    src = src === undefined ? opts.source : src;
    opts.range = true;
    if (typeof src !== 'string') src = String(src);

    try {
        var ast = parse(src, opts);
    } catch (err) {
        // console.log("error trying to parse "  + err + src);
        return undefined;
    }

    var result = {
        chunks: src.split(''),
        oldchunks: src.split(''),
        toString: function() {
            return result.chunks.join('')
        },
        inspect: function() {
            return result.toString()
        }
    };
    var index = 0;

    (function walk(node, parent) {
        insertHelpers(node, parent, result.chunks, result.oldchunks);

        forEach(objectKeys(node), function(key) {
            if (key === 'parent') return;

            var child = node[key];
            if (isArray(child)) {
                forEach(child, function(c) {
                    if (c && typeof c.type === 'string') {
                        walk(c, node);
                    }
                });
            } else if (child && typeof child.type === 'string') {
                insertHelpers(child, node, result.chunks, result.oldchunks);
                walk(child, node);
            }
        });
        fn(node);
    })(ast, undefined);

    return result;
};

function insertHelpers(node, parent, chunks, oldchunks) {
    if (!node.range) return;

    node.parent = parent;

    node.source = function() {
        return chunks.slice(
            node.range[0], node.range[1]
        ).join('');
    };
    node.oldsource = function() {
        return oldchunks.slice(
            node.range[0], node.range[1]
        ).join('');
    };
    if (node.update && typeof node.update === 'object') {
        var prev = node.update;
        forEach(objectKeys(prev), function(key) {
            update[key] = prev[key];
        });
        node.update = update;
    } else {
        node.update = update;
    }

    function update(s) {
        chunks[node.range[0]] = s;
        for (var i = node.range[0] + 1; i < node.range[1]; i++) {
            chunks[i] = '';
        }
    };

}