As @slebetman stated, In the original implementation of node.js it was asynchronous. However, console.log() was made synchronous some time in version 4 (2015). The reason for it was to avoid losing logs when a node process crashes. Making it synchronous ensures that all the text of the log gets printed before the process dies.

Note: However, 3rd party logging libraries like Winston or syslog may still be asynchronous. Some may be configured to be sync or async. The built-in console.log() is synchronous.