[JavaScript] +function () {} function

[JavaScript] +function () {} function

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In JS, often encounter the following code, exactly in the function before adding a unary operator, what role?
The function is to turn the functions into self-executing functions

+function   ()  {} () ;   

The plus sign here can be substituted for ~ , * , + , - , ! other unary operators,

The effect is equivalent to:

 (function  ()  { Span class= "hljs-built_in" style= "color: #268bd2;" >console . Log ( "foo!" ); })(); //or  (function  ()  {console . Log ( "foo!" ); }());

Without this plus, the parser will assume that function is the beginning of a declaration of functions, and the latter () will result in a syntax error.
With the + sign in front of the function, it becomes a functional expression, and a function expression adds another () to become a function that executes immediately.

[JavaScript] +function () {} function