Watch Options

You can configure the how TypeScript --watch works. This section is mainly for handling case where fs.watch and fs.watchFile have additional constraints like on Linux. You can read more at Configuring Watch.

watchFile

• Allowed: fixedpollinginterval,prioritypollinginterval,dynamicprioritypolling,fixedchunksizepolling,usefsevents,usefseventsonparentdirectory

• Released: 3.8

The strategy for how individual files are watched.

• fixedPollingInterval: Check every file for changes several times a second at a fixed interval.
• priorityPollingInterval: Check every file for changes several times a second, but use heuristics to check certain types of files less frequently than others.
• dynamicPriorityPolling: Use a dynamic queue where less-frequently modified files will be checked less often.
• useFsEvents (the default): Attempt to use the operating system/file system's native events for file changes.
• useFsEventsOnParentDirectory: Attempt to use the operating system/file system's native events to listen for changes on a file's parent directory

watchDirectory

• Allowed: usefsevents,fixedpollinginterval,dynamicprioritypolling,fixedchunksizepolling

• Released: 3.8

The strategy for how entire directory trees are watched under systems that lack recursive file-watching functionality.

• fixedPollingInterval: Check every directory for changes several times a second at a fixed interval.
• dynamicPriorityPolling: Use a dynamic queue where less-frequently modified directories will be checked less often.
• useFsEvents (the default): Attempt to use the operating system/file system's native events for directory changes.

fallbackPolling

• Allowed: fixedinterval,priorityinterval,dynamicpriority,fixedchunksize

• Released: 3.8

When using file system events, this option specifies the polling strategy that gets used when the system runs out of native file watchers and/or doesn't support native file watchers.

• fixedPollingInterval: Check every file for changes several times a second at a fixed interval.
• priorityPollingInterval: Check every file for changes several times a second, but use heuristics to check certain types of files less frequently than others.
• dynamicPriorityPolling: Use a dynamic queue where less-frequently modified files will be checked less often.
• synchronousWatchDirectory: Disable deferred watching on directories. Deferred watching is useful when lots of file changes might occur at once (e.g. a change in node_modules from running npm install), but you might want to disable it with this flag for some less-common setups.

synchronousWatchDirectory

• Released: 3.8

Synchronously call callbacks and update the state of directory watchers on platforms that don`t support recursive watching natively. Instead of giving a small timeout to allow for potentially multiple edits to occur on a file.

{
  "watchOptions": {
    "synchronousWatchDirectory": true
  }
}

excludeDirectories

• Released: 4.2

You can use excludeFiles to drastically reduce the number of files which are watched during --watch. This can be a useful way to reduce the number of open file which TypeScript tracks on Linux.

{
  "watchOptions": {
    "excludeDirectories": ["**/node_modules", "_build", "temp/*"]
  }
}

excludeFiles

• Released: 4.2

You can use excludeFiles to remove a set of specific files from the files which are watched.

{
  "watchOptions": {
    "excludeFiles": ["temp/file.ts"]
  }
}