JavaScript加号在函数名前面

问题描述

   + ，它使它成为一个函数表达式，这意味着该名称是可选的，并且可以引用该函数，该函数可以是所以括号是有效的。 
 
 
  + 只是其中一个选项。它也可以是  -  ，！，〜或几乎任何其他一元运营商。或者，你可以使用圆括号（这是比较常见的，但在句法上既不多也不少）：
 
 pre $ （function（）{ console.log（Foo！）;}）（）; 
 //或
（function（）{console.log（Foo！）;}（））; 
  

I've been looking on info about self-invoking functions, and somewhere I stumbled on this notation:

+function(){}

Can someone explain to me what the + sign in front of the function means/does?

解决方案

It forces the parser to treat the part following the + as an expression. This is usually used for functions that are invoked immediately, e.g.:

+function() { console.log("Foo!"); }();

Without the + there, if the parser is in a state where it's expecting a statement (which can be an expression or several non-expression statements), the word function looks like the beginning of a function declaration rather than a function expression and so the () following it (the ones at the end of the line above) would be a syntax error (as would the absense of a name, in that example). With the +, it makes it a function expression, which means the name is optional and which results in a reference to the function, which can be invoked, so the parentheses are valid.

+ is just one of the options. It can also be -, !, ~, or just about any other unary operator. Alternately, you can use parentheses (this is more common, but neither more nor less correct syntactically):

(function() { console.log("Foo!"); })();
// or
(function() { console.log("Foo!"); }());

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