Compare set to null vs delete member in NodeJS

results.txt

NodeJS 0.8.x on MBP:

$ node delete.js 
89300 'value to null'
3100674 'deleting member'

test.js

var microtime = require('microtime'),
    i,
    t,
    obj,
    max = 10000000;

function run1(obj) {
    obj.foo = null; // seeting value to falsy

    t = microtime.now();
    for (i = 0; i < max; i += 1) {
        if (obj.foo) {
            obj.foo();
        }
    }
    console.log(microtime.now() - t, 'value to null');
}

function run2(obj) {
    delete obj.foo; // deleting member

    t = microtime.now();
    for (i = 0; i < max; i += 1) {
        if (obj.foo) {
            obj.foo();
        }
    }
    console.log(microtime.now() - t, 'deleting member');
}


run1({
    foo: function () {
        var f = 1;
    },
    bar: 1
});
run2({
    foo: function () {
        var f = 1;
    },
    bar: 1
});