Specific use of Node.js package manager npm

Purpose

Current Node.js installation packages all come with an important tool package manager npm . npm has two main functions: downloading and managing third-party modules; building and running projects. The use of npm itself is not complicated, but it is not worry-free to use it in the mainland's network environment, and it adds a lot of workload. This article will explain the relevant content.

npm init and package.json files

There is usually a package.json file in the root directory of a Node.js project. This file mainly configures project-related information, including project name, version number, entry file, required modules, and other information. This file can be created manually, but it is usually generated using the npm init command (you can also use npm init -y to skip the query phase and generate a package.json file with default parameters):

Usually the package.json file contains many fields, such as the following:

{
  "name": "naisu",
  "version": "1.0.0",
  "description": "lalala",
  "main": "index.js",
  "scripts": {
    "start": "node index.js"
  },
  "author": "nx",
  "license": "ISC",
  "dependencies": {
    "electron-squirrel-startup": "^1.0.0",
    "serialport": "^9.2.4"
  },
  "devDependencies": {
    "electron": "15.1.1",
    "electron-rebuild": "^3.2.3"
  }
}

Some of the fields are relatively important, and the relevant descriptions are as follows:

nameProject name

version version number

main project main entry file

scripts npm run command script For example, if "start": "node index.js" is configured above, we can use npm run start in the terminal to execute the node index.js command (the four commands start/stop/test/restart can omit run), which is very useful when complex commands need to be executed;

dependencies Modules that the project depends on to run
devDependencies required for project development
These two fields store the module names and versions that the project depends on. With this information, you can use npm install to install these modules into the project .

Module installation and management

Installing the Module

Module installation uses npm install <packageName> . For example, the cowsay module is installed in the following demonstration:

When npm installs a module, it will also install the modules that the module depends on. By default, it will be installed in the node_modules folder under the directory. The installed modules will be recorded in the dependencies field of the package.json file, and the version information of the module and the dependent modules will be recorded in package-lock.json file.

When installing, you can add @版本號after the module name to install a specific version , such as npm install [email protected] .

If a module is already installed, it will not be reinstalled when the installation command is executed again. You can use the -f or --force option to force the installation : npm install --force <packageName> .

When installing, you can use the -S or --save option to mark the module as a dependencies (the default value) for the project to run; you can also use the -D or --save-dev option to mark the module as a devDependencies module required for project development, such as npm install --save-dev <packageName> .

Modules can also be installed globally using -g or --global option, such as npm install --global <packageName> .

install command in the installation module can also be abbreviated as i .

View installed modules

Use npm list to view the modules installed in the current directory and their dependencies.

Use -g or --global option to view globally installed module information, and use --depth=x to specify the viewing depth.

Update Module

Use npm update <packageName> to update the module. The options mentioned above, such as --save --save-dev --global can also be used here.

Deleting a module

Use npm uninstall <packageName> to uninstall a module.
Use the -g or --global option to unload global modules.

npx

npx is a tool included in the new version of npm (since 5.2), which is mainly used to run modules: if the module exists in the project directory or system environment, run the module directly. If not, there is no need to install it. npx will download it to a temporary directory and then run it.

Module compilation

Some third-party modules are developed in other languages. These modules cannot be run directly and need to be compiled for the operating environment before they can be used. This requires compilation tools, the most common of which are node-gyp and node-pre-gyp tools. For some modules on some platforms, some other tools may be required. For example, on the Windows platform, the windows-build-tools tool is often needed.

These tools can be installed and compiled when needed, and most of the time npm will handle these things automatically. Some platforms can also install these tools when installing Node.js. For example, on Windows platforms, you can check the installation options when installing Node.js:

It will install these tools after installing Node.js:

If you didn't check this option when you first installed Node.js, you can just reinstall it.

Version Control

package.json and package-lock.json files mentioned above record module-related information, one of the important information is the module version number.

The version number of a module or project in Node.js consists of three numbers separated by dots, which are major version , minor version , and patch version from left to right.

The version number rules themselves are nothing special, but there are many modifiers before and after the version numbers in npm management and package.json and package-lock.json files. These symbols specify the rules for module installation and update. The common rules are as follows:

• Without any modification: specify a specific version, such as 2.2.3 ;
• latest : use the latest available version;
• ^ : only updates that do not change the leftmost non-zero digit will be performed;
• ~ : will only update the patch version;
• > : accept any version higher than the specified version;
• < : accept any version lower than the specified version;
• = : accepts the exact version, can be used in combination with < > ;
• - : accept a certain range of versions, such as 2.1.0 - 2.6.2 ;
• || : combination, such as < 2.1 || > 2.6 ;

Change source

In the network environment of mainland China, module download and installation errors or failures often occur, resulting in the program not running correctly. You can try the following steps to reinstall:

• Clear npm cache clean --force ;
• Delete the node_modules folder and its contents;
• If there is package-lock.json file, you can also delete it (remember to back it up);
• Reinstall the module (if there is a package.json file, just npm install to install all modules in one step);

If the above method doesn't work, and there is no ladder or the ladder doesn't work, you can only try to change the source.

Use nrm tool to change source

The most convenient way to change npm sources is to use the nrm tool. You can use npm install -g nrm to install it globally, or you can directly use npx nrm . The common operations of nrm are as follows:

• nrm ls lists available sources and addresses;
• nrm test tests the available source speed;
• nrm use <registry> switch source;
• add <registry> <url> Add source;
• del <registry> delete source;

Use cnpm instead of npm

cnpm can be used to replace most of the work of npm , but it uses Taobao's mirror source, see: https://npmmirror.com/

You can install cnpm using npm install -g cnpm --registry=https://registry.npmmirror.com . When you use it later, just replace the place where npm is originally needed with cnpm.

Summarize

Node.js development is basically inseparable from the npm tool, but npm is also easy to use. The main problem you may encounter is network problems.

In addition to npm and the above cnpm, Yarn is also a common package management tool in Node.js. For more information, please refer to its official link: https://classic.yarnpkg.com/lang/en/

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