带要求的双参数: var io = require('socket.io')(http); [英] Double parameters with require: var io = require('socket.io')(http);

问题描述

我是 node 和 JS 的新手，正在研究 socket.io 聊天示例 (http://socket.io/get-started/chat/).我在服务器中遇到了这段代码:

I'm new to node and JS and was working thorough the socket.io chat example (http://socket.io/get-started/chat/). I came across this code in the server:

var app = require('express')();
var http = require('http').Server(app);
var io = require('socket.io')(http);

我看过其他教程，之前从未见过 require 后的双括号.(http) 部分有什么作用?是 require 的参数，是不是改变了类型，还是别的什么?

I've looked at other tutorials and never seen double parentheses after require before. What does the (http)part do? Is it a parameter for require, doest it change the type, or something else?

谢谢！

推荐答案

在 JavaScript 中，函数是 一等公民.这意味着它可以被另一个函数返回.

In JavaScript, function is the First-class citizen. This means that it can be returned by another function.

考虑以下简单的例子来理解这一点:

Consider the following simple example to understand this:

var sum = function(a) {
    return function(b) {
        return a + b;
    }
}

sum(3)(2);  //5

//...or...

var func = sum(3);
func(2);   //5

在您的示例中，require('socket.io') 返回另一个函数，该函数立即使用 http 对象作为参数调用.

In your example, require('socket.io') returns another function, which is called immediately with http object as a parameter.

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