// OK [1, , 3].forEach(function(elt, idx) { console.log(idx + " is not omitted."); }); // NOT OK [1, , 3].forEach(function(elt, idx) { sum += elt; }); // NOT OK function f1(x, y) { return y; } f1(23, 42); // OK function f2(x, y) { return y; } [].map(f2); // OK function f3(x, y) { return y; } var g = f3; [].map(g); // OK define(function (require, exports, module) { module.x = 23; }); // OK: starts with underscore function f(_p) { }