In node, the global object is an object that can be used directly without reference. It can be divided into: 1. Global objects used for module packaging; 2. Process objects; 3. Console module; 4 , EventLoop related API; 5. Buffer object; 6. global.
The operating environment of this tutorial: windows10 system, nodejs version 12.19.0, Dell G3 computer.
The global object is an object that can be used directly without a reference. It should be noted that the global object is different from the global keyword.
nodejs global objects are divided into the following categories:
1. Global objects used for module packaging
(1 ) exports
(2) module
(3) require
(4)__filename: current file name
(5)__dirname: current file directory
2. Process object
3. Console module
4. EventLoop related api
(1)setImmediate
(2)setInterval
(3)setTimeout
(4)Related clear
5. Buffer object
6.global
All global variables (except global itself) are attributes of the global object
Can handle binary and non-Unicode encoded data
The original data is stored in the Buffer class instantiation. Buffer is similar to an integer array, and memory is allocated to it in the V8 heap original storage space
Once a Buffer instance is created, the size cannot be changed
Process object, provides information and control about the current process
Included in the process of executing the node program, if parameters need to be passed, we want to obtain this parameter need to be in the process built-in object
Start the process:
node index.js 参数1 参数2 参数3
The index.js file is as follows:
process.argv.forEach((val, index) => {
console.log(`${index}: ${val}`);});The output is as follows:
/usr/local/bin/node/Users/mjr/work/node/process-args.js 参数1参数2参数3
In addition, it also includes some other information such as version and operating system Wait
Used to print stdout and stderr
The most commonly used way to input content: console .log
console.log("hello");Clear the console: console.clear
console.clear
Print the call stack of the function: console.trace
function test() {
demo();}function demo() {
foo();}function foo() {
console.trace();}test();
Set timer and clear timer
setInterval(callback, delay[, ...args])
callback is executed repeatedly every delay milliseconds
clearInterval is the corresponding method for canceling the timer
Set delayer and clear delayer
setTimeout(callback,delay[,...args])
callback is executed once after delay milliseconds
clearTimeout is the method corresponding to canceling the delayer
Global namespace object, the process, console, setTimeout, etc. mentioned on the wall are all placed in global中
console.log(process === global.process) // true
These global objects are variables in the module, but each module has them. They look like global variables, like in It cannot be used in command interaction, including:
Get the path of the current file, excluding the following file name
Run node example.js from /Users/mjr:
console.log(__dirname);// 打印: /Users/mjr
Get the path and file name of the current file, including the subsequent file name
Run node example from /Users/mjr. js:
console.log(__filename);// 打印: /Users/mjr/example.js
module.exports is used to specify the content exported by a module, that is, the content that can be accessed through require()
exports.name = name;exports.age = age;exports.sayHello = sayHello;
The reference to the current module is used to specify the content exported by a module through module.exports, that is, the content that can be accessed through require()
Used to import modules, JSON, or local files. Modules can be imported from node_modules.
You can use relative paths to introduce local modules or JSON files. The path will be processed according to the directory name defined by __dirname or the current working directory
Recommended learning: "nodejs video tutorial》
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