test.js

this.context.treePath = [1,2,3];

EAD.prototype.treePath = function() {
    var treePath = this.context.treePath;
    _.forEach(this.context.path, function(n) {
        if (treePath[n] === undefined) {
            treePath[n] = {};
        }
        treePath = treePath[n];
    }, this);
};