new_test.js

function SomeClass() {
    this.version = null;
    this.header_length = null;
    this.header_bytes = null;
    this.diffserv = null;
    this.total_length = null;
    this.identification = null;
    this.flags = {};
    this.fragment_offset = null;
    this.ttl = null;
    this.protocol = null;
    this.header_checksum = null;
    this.saddr = null;
    this.daddr = null;
    this.protocol_name = null;
    this.payload = null;
}

SomeClass.prototype.decode = function () {
    this.version = 4;
    this.header_length = 1;
    this.header_bytes = 2
    this.diffserv = 3;
    this.total_length = 4;
    this.identification = 5;
    this.flags.reserved = 6;
    this.flags.df = 7;
    this.flags.mf = 8;
    this.fragment_offset = 9;
    this.ttl = 10;
    this.protocol = 11;
    this.header_checksum = 12;
    this.saddr = 13;
    this.daddr = 14;
};

function SomeClass2() {
}

SomeClass2.prototype.decode = function () {
    this.version = 4;
    this.header_length = 1;
    this.header_bytes = 2
    this.diffserv = 3;
    this.total_length = 4;
    this.identification = 5;
    this.flags = {};
    this.flags.reserved = 6;
    this.flags.df = 7;
    this.flags.mf = 8;
    this.fragment_offset = 9;
    this.ttl = 10;
    this.protocol = 11;
    this.header_checksum = 12;
    this.saddr = 13;
    this.daddr = 14;
};

var start = Date.now();
for (var i = 0; i < 10000000; i++) {
    var a = new SomeClass().decode();
}
var dur = Date.now() - start;
console.log("init constructor in " + dur + "ms");

var start = Date.now();
for (var i = 0; i < 10000000; i++) {
    var a = new SomeClass2().decode();
}
var dur = Date.now() - start;
console.log("empty constructor in " + dur + "ms");

var start = Date.now();
for (var i = 0; i < 10000000; i++) {
    var a = new SomeClass().decode();
}
var dur = Date.now() - start;
console.log("init constructor in " + dur + "ms");

var start = Date.now();
for (var i = 0; i < 10000000; i++) {
    var a = new SomeClass2().decode();
}
var dur = Date.now() - start;
console.log("empty constructor in " + dur + "ms");

out.txt

$ node ./new_test.js 
init constructor in 884ms
empty constructor in 1103ms
init constructor in 1073ms
empty constructor in 1263ms