index.js

module.exports = Traverse;
function Traverse (obj) {
    if (!(this instanceof Traverse)) return new Traverse(obj);
    this.value = obj;
}

Traverse.prototype.get = function (ps) {
    var node = this.value;
    for (var i = 0; i < ps.length; i ++) {
        var key = ps[i];
        if (!Object.hasOwnProperty.call(node, key)) {
            node = undefined;
            break;
        }
        node = node[key];
    }
    return node;
};

Traverse.prototype.set = function (ps, value) {
    var node = this.value;
    for (var i = 0; i < ps.length - 1; i ++) {
        var key = ps[i];
        if (!Object.hasOwnProperty.call(node, key)) node[key] = {};
        node = node[key];
    }
    node[ps[i]] = value;
    return value;
};

Traverse.prototype.map = function (cb) {
    return walk(this.value, cb, true);
};

Traverse.prototype.forEach = function (cb) {
    this.value = walk(this.value, cb, false);
    return this.value;
};

Traverse.prototype.reduce = function (cb, init) {
    var skip = arguments.length === 1;
    var acc = skip ? this.value : init;
    this.forEach(function (x) {
        if (!this.isRoot || !skip) {
            acc = cb.call(this, acc, x);
        }
    });
    return acc;
};

Traverse.prototype.deepEqual = function (obj) {
    var equal = true;
    var node = obj;
    
    this.forEach(function (y) {
        var notEqual = (function () {
            equal = false;
            //this.stop();
        }).bind(this);
        
        if (this.key) node = node[this.key];
        var x = node;
        
        this.post(function () {
            node = x;
        });
        
        var toS = function (o) {
            return Object.prototype.toString.call(o);
        };
        
        if (this.circular) {
            if (Traverse(obj).get(this.circular.path) !== x) notEqual();
        }
        else if (typeof x !== typeof y) {
            notEqual();
        }
        else if (x.__proto__ !== y.__proto__) {
            notEqual();
        }
        else if (x === y) {
            // nop
        }
        else if (typeof x === 'function') {
            if (x instanceof RegExp) {
                // both regexps on account of the __proto__ check
                if (x.toString() != y.toString()) notEqual();
            }
            else if (x !== y) notEqual();
        }
        else if (typeof x === 'object') {
            if (x === null || y === null) {
                if (x !== y) notEqual();
            }
            else if (toS(y) === '[object Arguments]'
            || toS(x) === '[object Arguments]') {
                if (toS(x) !== toS(y)) {
                    notEqual();
                }
            }
            else if (x instanceof Date || y instanceof Date) {
                if (!(x instanceof Date) || !(y instanceof Date)
                || x.getTime() !== y.getTime()) {
                    notEqual();
                }
            }
            else {
                var kx = Object.keys(x);
                var ky = Object.keys(y);
                if (kx.length !== ky.length) return false;
                for (var i = 0; i < kx.length; i++) {
                    var k = kx[i];
                    if (!Object.hasOwnProperty.call(y, k)) {
                        notEqual();
                    }
                }
            }
        }
    });
    
    return equal;
};

Traverse.prototype.paths = function () {
    var acc = [];
    this.forEach(function (x) {
        acc.push(this.path); 
    });
    return acc;
};

Traverse.prototype.nodes = function () {
    var acc = [];
    this.forEach(function (x) {
        acc.push(this.node);
    });
    return acc;
};

Traverse.prototype.clone = function () {
    var parents = [], nodes = [];
    
    return (function clone (src) {
        for (var i = 0; i < parents.length; i++) {
            if (parents[i] === src) {
                return nodes[i];
            }
        }
        
        if (typeof src === 'object' && src !== null) {
            var dst = copy(src);
            
            parents.push(src);
            nodes.push(dst);
            
            Object.keys(src).forEach(function (key) {
                dst[key] = clone(src[key]);
            });
            
            parents.pop();
            nodes.pop();
            return dst;
        }
        else {
            return src;
        }
    })(this.value);
};

function walk (root, cb, immutable) {
    var path = [];
    var parents = [];
    
    return (function walker (node_, index) {
        var node = immutable ? copy(node_) : node_;
        var modifiers = {};
        
        var state = {
            node : node,
            node_ : node_,
            ancestors: [].concat(parents.slice(0, parents.length - 1)),
            path : [].concat(path),
            parent : parents.slice(-1)[0],
            key : path.slice(-1)[0],
            isRoot : path.length === 0,
            level : path.length,
            circular : null,
            index: index || 0,
            update : function (x) {
                if (!state.isRoot) {
                    state.parent.node[state.key] = x;
                }
                state.node = x;
            },
            'delete' : function () {
                delete state.parent.node[state.key];
            },
            remove : function () {
                if (Array.isArray(state.parent.node)) {
                    state.parent.node.splice(state.key, 1);
                }
                else {
                    delete state.parent.node[state.key];
                }
            },
            before : function (f) { modifiers.before = f },
            after : function (f) { modifiers.after = f },
            pre : function (f) { modifiers.pre = f },
            post : function (f) { modifiers.post = f }
        };
        
        if (typeof node == 'object' && node !== null) {
            state.isLeaf = Object.keys(node).length == 0
            
            for (var i = 0; i < parents.length; i++) {
                if (parents[i].node_ === node_) {
                    state.circular = parents[i];
                    break;
                }
            }
        }
        else {
            state.isLeaf = true;
        }
        
        state.notLeaf = !state.isLeaf;
        state.notRoot = !state.isRoot;
        
        // use return values to update if defined
        var ret = cb.call(state, state.node);
        if (ret !== undefined && state.update) state.update(ret);
        if (modifiers.before) modifiers.before.call(state, state.node);
        
        if (typeof state.node == 'object'
        && state.node !== null && !state.circular) {
            parents.push(state);
            
            var keys = Object.keys(state.node);
            keys.forEach(function (key, i) {
                path.push(key);
                
                if (modifiers.pre) modifiers.pre.call(state, state.node[key], key);
                
                var child = walker(state.node[key], i);
                if (immutable) state.node[key] = child.node;

                child.isLast = i == keys.length - 1;
                child.isFirst = i == 0;
                                
                if (modifiers.post) modifiers.post.call(state, child);
                
                path.pop();
            });
            parents.pop();
        }
        
        if (modifiers.after) modifiers.after.call(state, state.node);
        
        return state;
    })(root).node;
}

Object.keys(Traverse.prototype).forEach(function (key) {
    Traverse[key] = function (obj) {
        var args = [].slice.call(arguments, 1);
        var t = Traverse(obj);
        return t[key].apply(t, args);
    };
});

function copy (src) {
    if (typeof src === 'object' && src !== null) {
        var dst;
        
        if (Array.isArray(src)) {
            dst = [];
        }
        else if (src instanceof Date) {
            dst = new Date(src);
        }
        else if (src instanceof Boolean) {
            dst = new Boolean(src);
        }
        else if (src instanceof Number) {
            dst = new Number(src);
        }
        else if (src instanceof String) {
            dst = new String(src);
        }
        else {
            dst = Object.create(src.__proto__);
        }
        
        Object.keys(src).forEach(function (key) {
            dst[key] = src[key];
        });
        return dst;
    }
    else return src;
}