Javascript brackets have five semantics

**Semantics 1, function declaration when the parameter table **

function func(arg1,arg2){
  // ...
}

**Semantics 2, used in conjunction with statements to achieve certain qualifiers **

//Used with for in
for(var a in obj){
  // ...
}

//Use it with if
if(boo){
  //...
}

//Use it with while
while(boo){
  // ...
}

//Used with do while
do{
  // ...
}while(boo)

Note: when used with if, while, and do while, the parentheses implicitly convert the result of the expression into a Boolean value. See implicit type conversion in JavaScript.

**Semantics 3, used with new to pass values (arguments) **

//Let's say I've defined the class Person, and it has two fields name, age
var p1 = new Person('Jack',26);

**Semantics 4, as a function or object method call operator (if defined parameters can also be passed as semantics 3) **

//Let's say I've defined the function func
func();

//Assume that you've defined the object obj and have the func method
obj.func();

Here’s the typeof operator, which some people like to use

The typeof (XXX);

Note that the parentheses after typeof are not semantics 4 (that is, not a function call), but semantics 5 as mentioned later. I use typeof without the usual parentheses.

Semantic 5, force expression operation

The most familiar thing about semantic 5 is that you use eval to parse JSON

function strToJson(str){
     //In eval, we have the forced operator () on both sides of a string
     var json = eval('(' + str + ')'); 
     return json;
}

Another example is the use of more anonymous function self - execution

(function(){
  // ...
})();