> For the complete documentation index, see [llms.txt](https://jen-hsuan-hsieh.gitbook.io/javascript-node-js/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jen-hsuan-hsieh.gitbook.io/javascript-node-js/chapter1/12javascript-quan-gong-lve-ff1a-ke-fu-js-de-qi-guai-bu-fen/121zhi-xing-huan-jing-yu-ci-hui-huan-jing/1215dan-zhi-xing-xu-3001-tong-bu-zhi-xing.md).

# 1.2.1.5.單執行緒、同步執行

* JavaScript是單執行緒且同步執行的
* 單執行緒 (Single thread)
  * 一次執行一個指令
* 同步執行 (Sychronous)
  * 一次執行一行code