Differences between .call(this) and () on a immediately self invoking function

Question

I came across this code in one of our online AngularJS apps, and was wondering what this does. Is it different than just calling a immediately self invoking function with parenthesis.

(function() {

}).call(this); // What was in TFS

vs

(function() {

})(); // Are these the same?

Is there any benefits of calling one over the other, or is it merely coding preference?

Answer 1

They're very different. The first uses whatever the current this is (at global scope, this is a reference to the global object; in other scopes, it could be just about anything). The second will use the default this, which is a reference to the global object in loose mode but undefined in strict mode.

Gratuitous example :-) :

console.log("At global scope:");
(function() {
  console.log(this === window); // true
}).call(this); // What was in TFS
(function() {
  console.log(this === window); // true
})();
(function() {
  "use strict";
  console.log(this === window); // false (this === undefined)
})();

console.log("Not at global scope:");
(function() {
  (function() {
    console.log(this === window); // false
  }).call(this); // What was in TFS
  (function() {
    console.log(this === window); // true
  })();
}).call({});// Using something other than the default

.as-console-wrapper {
  max-height: 100% !important;
}