请教jquery.validate.js中自执行函数语法：第二个函数是否为factory参数

Great question! Let’s break this down clearly to confirm your suspicion: yes, the function($) { ... } block is indeed the factory argument passed to the first function.

This is a classic Immediately Invoked Function Expression (IIFE) pattern, commonly used in jQuery plugins to encapsulate code, avoid global scope pollution, and support multiple module loading systems. Let’s unpack the structure piece by piece:

Step 1: The Outer Wrapper Function #

First, we have the outer function definition (wrapped in parentheses to make it an expression instead of a declaration):

(function (factory) {
  alert("In jquery.validate.js factory");
  if ( typeof define === "function" && define.amd ) {
    // AMD environment (like RequireJS): load jQuery and pass it to the factory
    define( ["jquery"], factory );
  } else {
    // Non-AMD environment: use the global jQuery object
    factory( jQuery );
  }
})

This function accepts a single parameter called factory — which is expected to be a function that takes jQuery (aliased as $) as its own parameter.

Step 2: The Factory Function (Your Question’s Focus) #

Right after the outer wrapper, we have another function wrapped in parentheses — this is the actual argument being passed to the outer function’s factory parameter:

(function ($) {
  ... // The core jQuery.validate.js code lives here
})

How It All Works Together #

When the code runs, the outer function is immediately invoked, and the inner function($) { ... } is passed into it as the factory variable. Then:

• If an AMD loader (like RequireJS) is present, it uses define to load the "jquery" module, then calls the factory function with the loaded jQuery object.
• If no AMD loader exists, it directly calls factory( jQuery ), passing the global jQuery object into the inner function (where it’s aliased as $ to avoid conflicts).

Simplified Example to Illustrate #

To make this even clearer, here’s a stripped-down version of the same pattern:

// Outer function that accepts a factory parameter
(function(factory) {
  // Call the factory with a value
  factory("Hello from outer function!");
})(
  // This function is the factory argument
  function(message) {
    console.log(message); // Logs: "Hello from outer function!"
  }
);

This is exactly the same structure as the jQuery.validate code — the second function is always the argument passed to the first.

Why This Pattern Is Used #

• Encapsulation: Keeps all the plugin code inside the inner function, so it doesn’t leak variables into the global scope.
• Alias Safety: Ensures $ refers to jQuery inside the plugin, even if the global $ is overwritten by another library.
• Module Compatibility: Supports both global jQuery usage and modern module loaders (AMD) without changing the core plugin code.

内容的提问来源于stack exchange，提问作者root44