Learn Nodejs from me (3) --- Node.js module_javascript skills

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/. These core modules are compiled into binary files and can require('module name') Get it; 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 I am mainly talking 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; with Starting with "/" means loading with an absolute path, starting with "./" and starting with "../" means loading with a relative path, and starting with "./" means loading files in the same directory,

As mentioned earlier, 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

Copy code The code is as follows:

var outputVal = 0; //Output value
var increment = 1; //Increment
/* Set the output value*/
function seOutputVal (val) {
outputVal = val;
}
/* Set the increment*/
function setIncrement(incrementVal){
increment = incrementVal;
}
/* output*/
function printNextCount()
{
outputVal = increment;
console. log(outputVal) ;
}
function printOutputVal() {
console.log(outputVal);
}
exports.seOutputVal = seOutputVal;
exports.setIncrement = setIncrement;
module.exports.printNextCount = printNextCount;
Custom module example source code

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

Call custom module

Copy code The code is as follows:

/*
A Node.js file is a Module, this file may be Javascript code, JSON, or a compiled C/C extension.
Two important objects:
require is to obtain the module from the outside
exports is to expose the module interface
*/
var counter = require('./1_modules_custom_counter');
console.log('First call to module [1_modules_custom_counter]');
counter.seOutputVal(10); //Set counting starting from 10
counter.setIncrement (10);
counter.printNextCount();
counter.printNextCount();
counter.printNextCount();
counter.printNextCount();
/*
require calling the same module multiple times Will not load repeatedly
*/
var counter = require('./1_modules_custom_counter');
console.log('Second call to module [1_modules_custom_counter]');
counter.printNextCount( );
Custom mode calling source code

When running, you can find that all methods exposed 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 if node.js calls the same module multiple times through requirerequire, it will not be loaded repeatedly. Node.js will cache all loaded file modules based on the file name, so it will not be reloaded

Note: Caching by file name refers to the actual file name, and it will not be considered a different file just because the incoming path form is different.

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

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

The answer is: TypeError: Object #