Learn Nodejs with me--- Node.js module

Introduction and Information

Through the official API of Node.js, you can see that Node.js itself provides many core modules http://nodejs.org/api/, and these core modules are compiled into binary files , you can obtain it with require('module name'); the core module has the highest loading priority (this will be reflected when there is a module with the same name as the core module)

(This time we mainly talk about custom modules)

Node.js also has a type of module called a file module, which can be a JavaScript code file (.js as the file suffix), a JSON format text file (.json as the file suffix), or an edited C/C++ File (.node as file suffix);

The file module access method is through require('/filename.suffix') require('./filename.suffix') requrie('../filename. suffix') to access, the file suffix can be omitted; starting with "/" means loading with an absolute path, starting with "./" and starting with "../" means loading with a relative path, and starting with "./" Indicates files in the same directory,

mentioned earlier that the file suffix can be omitted, Nodejs tries to load the priority js file > json file > node file

Create a custom module

Take a counter as an example

var outputVal  = 0;     //输出值
var increment = 1;    //增量
/* 设置输出值 */
function seOutputVal (val) {
    outputVal = val;
}
/* 设置增量 */
function setIncrement(incrementVal){
    increment = incrementVal;
}
/* 输出 */
function printNextCount()
{    
    outputVal += increment;
    console.log(outputVal) ;
}
function printOutputVal() {
    console.log(outputVal);
}
exports.seOutputVal = seOutputVal;
exports.setIncrement = setIncrement;
module.exports.printNextCount = printNextCount;
自定义模块 示例源码

The focus of the example is exports and module.exports; it provides an interface for external access. Let’s call it below to see the effect

Call the custom module

/*
    一个Node.js文件就是一个模块，这个文件可能是Javascript代码、JSON或者编译过的C/C++扩展。
    重要的两个对象：
    require是从外部获取模块
    exports是把模块接口公开    
*/
var counter = require('./1_modules_custom_counter');
console.log('第一次调用模块[1_modules_custom_counter]');
counter.seOutputVal(10);               //设置从10开始计数
counter.setIncrement (10);             //设置增量为10
counter.printNextCount();
counter.printNextCount();
counter.printNextCount();
counter.printNextCount();
/*
    require多次调用同一模块不会重复加载
*/
var counter = require('./1_modules_custom_counter');
console.log('第二次调用模块[1_modules_custom_counter]');
counter.printNextCount();
自定义模式调用 源码

When running, you can find that all the methods exposed to the outside through exports and module.exports can be accessed!

As you can see in the example, I obtained the module through require('./1_modules_custom_counter') twice, but the printNextCount() method did start from 60 after the second reference~~~

The reason is that node.js will not load the same module multiple times through requirerequire. Node.js will cache all loaded file modules according to the file name, so it will not be reloaded

Note: By file name The cache refers to the actual file name, and it will not be recognized as a different file because the incoming path form is different

There is a printOutputVal() method in the 1_modules_custom_counter file I created, which does not pass exports Or module.exports provides external public access methods,

What will happen if the 1_modules_load file is directly accessed and run?

The answer is: TypeError: Object #