Today, NPM install always reports an error: unable to verify the first certificate. After checking, it is found that

As of February 27, 2014, npm no longer supports its self-signed certificates. 

On February 27, 2014, NPM no longer supported self signed certificates

Because NPM install follows the HTTPS protocol, it needs to be guaranteed by digital certificates

Solution 1:

Cancel SSL validation: NPM config set strict SSL false

If not, replace the NPM source with a domestic image:
NPM config set registry   http://registry.cnpmjs.org/
npm config set registry   http://registry.npm.taobao.org/

Solution 2:

Upgrade: NPM install NPM – G — Ca = null
or NPM config set CA = “”

Recommended usage 1