Because semicolons at the ends of statements are optional, starting function call arguments on a separate line makes the code confusing. It could lead to errors and most likely will lead to questions for maintainers.

What was the initial intent of the developer?

  1. Define a function and then execute some unrelated code inside a closure ?
  2. Pass the second function as a parameter to the first one ?

The first option will be the one chosen by the JavaScript interpreter.

By extension, and to improve readability, any kind of function call argument should not start on new line.

Noncompliant Code Example

var fn = function () {
  //...
}

(function () { // Noncompliant
  //...
})();

Compliant Solution

Either

// define a function
var fn = function () {
  //...
}; // <-- semicolon added

// then execute some code inside a closure
(function () {
  //...
})();

Or

var fn = function () {
  //...
}(function () { // <-- start function call arguments on same line
  //...
})();