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newless

Modify constructors to function without <code>new</code>.

Newless

Newless is a super-simple JavaScript library that allows you to modify or create constructor functions that don't need to be called with new. This makes your code more safe and allows constructors to be used in more functional contexts (such as Array.map).

You can use it on a constructor while creating it:

var MyObject = newless(function(something) {
  this.setSomething(something);
});
 
MyObject.prototype.setSomething = function(value) {
  this.something = value;
};
 
var instance = MyObject("Hello");
instance.something; // "Hello" 

And, of course, on new ES 6/2015 style classes:

var MyObject = newless(class {
  constructor(something) {
    this.setSomething(something);
  }
  setSomething(value) {
    this.something = value;
  }
});
 
var instance = MyObject("Hello");
instance.something; // "Hello" 

You can also use it with existing constructors from other libraries without disrupting them:

var Map = newless(google.maps.Map);
var map = Map(document.getElementById("map-canvas"), options);
// or 
var User = newless(Backbone.Model.extend({...}));
var user = User({name: "Jennifer"});

Note: this description is long only because the caveat is uncommon and nuanced. In most cases, it shouldn’t affect you. :)

When an ES 2015 class is wrapped with Newless, you should be somewhat careful in trying to call it with a custom context via Class.call(customContext) or Class.apply(customContext). Because of limitations imposed by the class syntax, calling a Newless ES 2015 class will always return a new object. If the custom context you provide is one that includes the Newless class anywhere in its prototype chain, the returned object will have the exact same prototype chain as the custom context, but it will be separate object.

This is generally only an issue when creating a function constructor that inherits from a class constructor. Inheriting function constructors usually works like this:

function SubConstructor() {
  SuperConstructor.call(this);
  this.x = "some instance value";
}
SubConstructor.prototype = Object.create(SuperConstructor.prototype);

This works just fine when SuperConstructor is a normal constructor function or a Newless constructor function. If SuperConstructor is a class, this doesn’t work at all. However, if SuperConstructor is a Newless class, the are some minor oddities:

var superInstance;
var SuperConstructor = newless(class {
  constructor() {
    superInstance = this;
    this.y = "super constructor instance property";
  }
});
 
var instance = new SubConstructor();
 
// as you’d normally expect, all the properties are accessible: 
instance.x === "some instance value";
instance.y === "super constructor instance property";
 
// ...but technically, the `this` in the two constructors is not the same! 
instance !== superInstance;
Object.getPrototypeOf(instance) === superInstance;

You’ll notice above that the this used in SuperConstructor has become the prototype of the this used in SubConstructor. That’s done to make things work as smoothly as possible within the constraints created by ES 2015’s class syntax. You can avoid this slight oddity by instead coding SubConstructor like so:

function SubConstructor() {
  var instance = SuperConstructor.call(this);
  instance.x = "some instance value";
  return instance;
}
SubConstructor.prototype = Object.create(SuperConstructor.prototype);

Note that, instead of working with this, you work with the return value of calling SuperConstructor. If you already code inheritance this way, everything works fine. If you don’t, making this change could help you avoid some rare edge cases where you might run into trouble.

Newless is open source software. It is (c) 2013-2016 Rob Brackett and licensed under the BSD license. The full license text is in the LICENSE file.