How to detect that the script is running with npm or yarn?

In project development, it is common to use npm or yarn as package managers. To determine whether a script is executed using npm or yarn, you can inspect the environment variables, as both tools set specific environment variables during script execution.

Detection Method

1. Using Environment Variables

• npm: When executing a script with npm, it sets the environment variable npm_lifecycle_event to the name of the current script.
• yarn: When using yarn, it sets the environment variable npm_config_user_agent, which includes the string 'yarn'.

Example Code

javascript
if (process.env.npm_config_user_agent.includes('yarn')) {
    console.log('This script is run by Yarn');
} else if (process.env.npm_lifecycle_event) {
    console.log('This script is run by npm');
} else {
    console.log('Cannot determine the package manager');
}

Application Example

Suppose you are developing a Node.js project and wish to detect whether npm or yarn is used for different processing in your build script. You can integrate the above code into your build.js file to configure distinct build settings or execute specific preprocessing steps based on the package manager.

Important Notes

• Handle cases where environment variables are undefined to prevent runtime errors.
• This method depends on environment variables, and inconsistencies may arise in different versions or customized environments. Therefore, it is advisable to explicitly specify supported versions of npm or yarn within your project.

By this approach, you can easily identify the package manager used in the script, enabling more precise control and optimization.