The ambiguity of the parentheses "()" in Javascript

Javascript Small brackets have 5 semantics

Semantic 1: Parameter table when function declaration

1 function func (arg1, arg2) {
2//...
3}


Semantic 2: Used in conjunction with some statements to achieve certain qualifiers

1//And for use
2 for (var a in obj) {
3//...
4}
5
6//And if used together
7 if (boo) {
8//...
9}
10
11//And while working together
while (Boo) {
13//...
14}
15
16//And do while working together
do{
18//...
}while (Boo)

Note: When used with the IF, while, and do, the parentheses implicitly convert the result of the expression into a Boolean value. See implicit type conversions everywhere.



Semantics 3: Used with new to pass values (arguments)

Assuming that the class person is already defined, it has two field names (name), age
var p1 = new Person (' Jack ', 26);


Semantics 4: The invocation operator as a function or an object method (if a parameter is defined, it can be passed as an argument with semantic 3)

Assume that the function func has been defined
Func ();

Assume that the object obj is already defined and has the Func method
Obj.func ();
The typeof operator is mentioned here, and some people like to use it:

typeof (XXX);

Note that the parentheses after typeof are not semantic 4 (that is, not function calls), but rather the semantics 5 that are mentioned later. I use typeof generally without the parentheses in the back.
See also four ways to call named functions.



Semantics 5: Enforcing expression operations

As for semantic 5, the most familiar is the use of eval to parse JSON

1 function Strtojson (str) {
2//Eval strings are added with the mandatory operator ()
3 var json = eval (' (' + str + ') ');
4 return JSON;
5}
Another example is the use of anonymous function self-executing

1 (function () {
2//...
3}) ();
Note that the first pair of parentheses in the above code is semantic 5, while the second pair is semantic 4.

The ambiguity of the parentheses "()" in Javascript