diff --git a/envar-tool.js b/envar-tool.js
index 3d61220..33f3177 100644
--- a/envar-tool.js
+++ b/envar-tool.js
@@ -11,12 +11,12 @@ const assign_deep = require('assign-deep')
 const my = { envar: {} }
 
 module.exports = {
-  start_watching ({ envarFiles = ['./envar-base-dynamic.js', './envar-base-dynamic.gitignore.js'], rawEnvar = {} } = {}) {
-    chokidar.watch(envarFiles, { interval: 500 }).on('change', (onpath) => {
+  start_watching ({ envarFiles = ['./envar-base-dynamic.js', './envar-base-dynamic.gitignore.js'], rawEnvar = {}, interval = 1000 } = {}) {
+    chokidar.watch(envarFiles, { interval }).on('change', (onpath) => {
       // .on('all', (event, onpath)) 但这时，即使server刚启动，也会调用到这里一次
       console.log('envarTool.start_watching: envar file changed:', onpath)
-      delete require.cache[require.resolve(path.resolve(onpath))]
       try {
+        delete require.cache[require.resolve(path.resolve(onpath))]
         assign_deep(rawEnvar, require(path.resolve(onpath)))
         console.log(`envarTool.start_watching: successfully reload ${onpath}`)
       } catch (expt) {