Resolve possible strict violation (and help Batman save Gotham)

Question

I've got the following (simplified) Batman.js file:

(function(){
  "use strict";

  window.Batman = function(){
    // Global references
    this.version = "1.0.1";
  };

  Batman.prototype.saveGotham = function(params) {
    var _ = this; // Works fine
    destroyGotham.call(_, params);
  };

  // Private
  function destroyGotham(params){
    var _ = this; // <!-- "possible strict violation"
  }

}());

JSHint complains about a possible strict violation at the indicated line. How do I get around this without dropping the "use strict"?

P.S: I'd like the troublesome var _ = this to reference the Batman instance.

Answer 1

The value passed as this to a function in strict mode is not forced into being an object.
For a normal function, this is always an object, and it's the global object if called with an undefined or null this, in other words this is usually the window by default in non-strict mode.

Not only is automatic boxing a performance cost, but exposing the global object in browsers is a security hazard, because the global object provides access to functionality that "secure" JavaScript environments must restrict.
Thus for a strict mode function, the specified this is not boxed into an object, and if unspecified, this will be undefined by default.

This means that using this that way, just setting it to a variable

var _ = this;

in most cases will lead to this being undefined, which why jshint is saying it's a "possible" violation, as it would be if you didn't call it with call and provided a this-value.

Ignore jshint, what you're doing is fine.