安装npm本地包

There are two ways to install npm packages: locally or globally. You choose which kind of installation to use based on how you want to use the package.

If you want to depend on the package from your own module using something like Node's require, then you want to install locally. On the other hand, if you want to use it as a command line tool, something like the grunt CLI, then you want to install it globally.

安装

A package can be downloaded with the command npm install <package name>. For example:

npm install lodash

This will create the node_modules directory (if one doesn't exist yet), and will download the package to that directory.

Test: Run ls node_modules. You should see a lodash directory inside.

安装哪个版本的包?

If there is no package.json file in the local directory, the latest version of the package is installed.

If there is package.json file, the latest version satisfying the semver rule declared in package.json for that package (if there is any) is installed.

使用已安装包

Once the package is in node_modules, you can use it in your code. For example, if you are creating a Node module, you can require it.

Create a file named index.js, with the following code:

var lodash = require('lodash');

var output = lodash.without([1, 2, 3], 1);
console.log(output);

Test: Run the code using node index.js. It should output [2, 3].

使用 package.json 和 --save 标签

Another way to manage npm packages locally is to create a package.json file. If you have a package.json file in your directory and you run npm install, then npm will look at the dependencies that are listed in that file and download the latest versions satisfying semver rules for all of those. This is nice because it makes your build reproducible, which means that you can share it with other developers.

Create a file called package.json in your app directory.

{
    "name": "demo-app",
    "version": "1.0.0"
}

Download the package with the --save flag.

npm install lodash --save

This will download the package as before, but will also add it to the dependencies in package.json (unless it was already there).

Test: Check the dependencies key in package.json. lodash should be listed as a dependency.

手动添加依赖关系到 package.json

You can also add dependencies to package.json manually.

Add another package to your dependencies, e.g.:

"dependencies": {
    "lodash": "^2.4.1",
    "tap": "*"
}

Test: Run npm install, then ls node_modules. You should see a tap directory.

Note that if any package is already installed and satisfies the semver rule in package.json, running npm install will not update it to the latest version, even if there is one satisfying the same rule. In fact, no change is made to the package in this case, even if it was modified.

Thus, to reliably reinstall the latest versions of all packages satisfying the semver rules in package.json, delete the node_modules folder and run npm install.