Thoughts on separating declaration + definition in javascript

test1.js

// Usage:
//   var test = new Test(dep1, dep2);
//   test.publicMethod();

function Test(dep1, dep2) {
  var object = new TestClass();
  object.init(dep1, dep2);
  return object;
}

function TestClass() {
  this.dep1 = undefined;
  this.dep2 = undefined;
  this.privateVar = '123';
  this.privateMethod = function() {
    // ...
  }
}

TestClass.prototype.init = function(dep1, dep2) {
  this.dep1 = dep1;
  this.dep2 = dep2;
}

TestClass.prototype.publicMethod = function() {
  this.privateMethod();
  return this.privateVar;
}

test2.js

// Usage:
//   var test = new Test().init(dep1, dep2);
//   test.publicMethod();
// Or even:
//   new Test().init(dep1, dep2).publicMethod();

function Test() {
  this.dep1 = undefined;
  this.dep2 = undefined;
  this.privateVar = '123';
  this.privateMethod = function() {
    // ...
  }
}

Test.prototype.init = function(dep1, dep2) {
  this.dep1 = dep1;
  this.dep2 = dep2;
  return this;
}

Test.prototype.publicMethod = function() {
  this.privateMethod();
  return this.privateVar;
}