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Call a Function

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Overview

You can call a function from other parts of your Stitch application or from a connected client application.

Usage

The examples in this section demonstrate calling a simple function named sum that takes two arguments, adds them, and returns the result:

copy 
// sum: adds two numbers
exports = function(a, b) {
  return a + b;
};

Call from Another Function

You can call a function from another function, including incoming webhooks and triggers, by accessing function context with the context.functions global variable:

For additional information, see the Function Context reference page.

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// difference: subtracts b from a using the sum function
exports = function(a, b) {
    return context.functions.execute("sum", a, -1 * b);
};

Call from a JSON Expression

You can call a function from a Stitch JSON Expression, including service rules, by using the %function operator:

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{
  "numGamesPlayed": {
    "%function": {
      "name": "sum",
      "arguments": [
        "%%root.numWins",
        "%%root.numLosses"
      ]
    }
  }
}

Call from a Client Application

You can call a function from client applications that are connected with a Client SDK or over the wire protocol.

To execute a function from a JavaScript Client SDK, use the callFunction() method.

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const client = Stitch.defaultAppClient;
client.callFunction("sum", [3, 4]).then(result => {
    console.log(result) // Output: 7
});

To execute a function from the Android Client SDK, use the callFunction() method.

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StitchAppClient client = Stitch.getDefaultAppClient()
client.callFunction("sum", Arrays.asList(3, 4), BsonValue.class)
      .addOnCompleteListener(new OnCompleteListener<BsonValue>() {
        @Override
        public void onComplete(@NonNull final Task<BsonValue> task) {
          if (task.isSuccessful()) {
            Log.d("stitch", String.format("%s", task.getResult())); // Output: 7
          } else {
            Log.e("stitch", "Error calling function:", task.getException());
          }
        }
      });

To execute a function from the iOS Client SDK, use the callFunction(withName:withArgs:_:) method.

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let client = Stitch.defaultAppClient!
client.callFunction(withName: "sum", withArgs: [3, 4]) { (result: StitchResult<String>) in
    switch result {
    case .success(let sum):
        print(sum)
    case .failure(let error):
        print("Failed to calculate sum: \(String(describing: error))")
    }
}

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