What is the meaning of this code (0, function) in javascript [duplicate]

Question

I found this code in someone's code, it sound like this:

(0, function (arg) { ... })(this) 

After I try to play around like below,

(0, function (arg) { console.log(arg) })(2);  console.log((0, 1, 2, 3));  (0, function plus1 (arg) { console.log(arg + 1) }, function plus2 (arg) { console.log(arg + 2) })(5);

I found that it will always return last item in the bracket.

I wonder what is the name of this programming pattern and what is the use case?

Answer 1

In this particular case it seems superfluous, but sometimes this approach is useful.

For example, with eval:

(function() {    (0,eval)("var foo = 123"); // indirect call to eval, creates global variable  })();  console.log(foo);            // 123  (function() {    eval("var bar = 123");     // direct call to eval, creates local variable  })();  console.log(bar);            // ReferenceError

It's also useful when you want to call a method without passing the object as the this value:

var obj = {    method: function() { return this; }  };  console.log(obj.method() === obj);     // true  console.log((0,obj.method)() === obj); // false

Also note that, depending on the context, it might be the arguments separator instead of a comma operator:

console.log(    function(a, b) {      return function() { return a; };    }    (0, function (arg) { /* ... */ })(this)  ); // 0

Answer 2

typical example could be,

for(var i=0,j=10; i < j; i++){  // code ... } 

comma operator would evaluate expressions from left-to-right and return result of right most expression

// e.g.    var a = 1, b= 2, c = 3, d = function(){ console.log("a => " +  a) }()