Hello QiaoJiao,
Thank you for using EmEditor Professional!
Is “JavaScript” selected as the current configuration? You can confirm which configuration is selected in the Status Bar. If you see “JavaScript”, then it is selected. If you see another configuration name, such as HTML, then it will be highlighted only when surrounded by tag. To change the current configuration, you can double-click where you see a configuration name (such as “HTML”), and then you can select “JavaScript” on the menu you see. You can also check the file extension association on the Association tab of JavaScript properties, and make sure “JS” is included in the list.
Please let me know if you have further questions. Thank you.