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Build and test

A tool to selectively deploy only the Firebase Functions that changed.

functions-differ takes a list of Firebase Functions from your repository and returns a list of functions that changed since its last invocation. This helps you selectively deploy only the functions that changed, thus saving time during re-deployments.

It detects any changes to a function by bundling it into a single minified file, and calculating a hash for it. This works for changes in the function's code, change in its installed dependencies, or any other local imports.


  • Create a .differspec.json file in the directory containing your Firebase Functions:
    ├── firebase.json
    ├── functions
        ├── src
        └── .differspec.json 
  • Specify your function names and their paths in .differspec.json:
    "functions": {
        "login": "src/auth/login/function.ts",
        "register": "src/auth/login/function.ts"
  • Run functions-differ in the directory containing .differspec.json
cd my-firebase-project/functions
  • functions-differ will then output a list of functions that need to be (re)deployed. This includes any functions that were changed or added since its last invocation.
> functions-differ

The default output is suitable for passing to firebase deploy --only command.


functions-differ supports the following options:

Name Alias Description Default
dir d The directory containing .differspec.json file (current working directory)
write w Write output to .differspec.json file or not true
verbose v Output verbose logs false
prefix Prefix for each function name output functions:
sep Separator for each output function ,


.differspec.json serves as persistent storage for functions-differ. It contains the following properties:

Name Description
functions JSON object containing names of functions in the repository along with their paths
hashes (AUTOGENERATED, DO NOT MODIFY) JSON object containing hashes of all functions in the functions property
lastDiff (AUTOGENERATED, DO NOT MODIFY) JSON object containing the results of the last successful invocation of functions-differ
  • The functions property serves as an index of all functions present in your repository. functions-differ does not support automatic discovery of functions in the project (yet), and therefore this property is required.
  • The hashes and lastDiff properties are autogenerated by functions-differ, and should not be created/edited manually.


Please discuss bugs, feature requests, and help in Github Issues. Pull requests are welcome, but please make sure to open an issue for your changes first.


Install the package with npm:

npm install -g functions-differ


Tool to find Firebase Functions that changed for selective redeployments




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