If you are writing a lot of JavaScript/HTML, you might want to have a look at the following 2 free editors. Both incorporates real-time syntax checking & intelligent code completion.
1) Visual Studio Code - this is a lightweight editor from Microsoft, runs on MacOS, Windows, and Linux.
https://code.visualstudio.com/
2) Komodo Edit, also available for MacOS, Windows, and Linux
http://komodoide.com/komodo-edit