how to check header in nodejs express code example

Example 1: set headers in express

response.header("Access-Control-Allow-Origin", "*");
    response.header("Access-Control-Allow-Headers", "Origin, X-Requested-With,Content-Type, Accept");
    response.header('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE')

Example 2: hwo to cehck req header in js

var host = req.headers['host'];