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2.0.6 • Public • Published


Fitbit settings use React JSX that receives a props parameter. The JSX receives persisted settings from props.settings, and persists settings with props.settingStorage. In both cases the settings values must be strings. Values other than strings need to be 'packed' into strings with JSON.stringify() and 'unpacked' from strings with JSON.parse().

This library provides a wrapper to make it easier to work with Fitbit Setting API. Behind the scene, the wrapper 'packs' and 'unpacks' settings into / from strings, and persists to the props.settingsStorage, so that users don't need to do that in their codes.

By default, 'packs' always uses JSON.stringify() to encode settings, even if the value is a string, and 'unpacks' always attempts to decode strings with JSON.parse() and, if that fails, return the strings as is. This default behaviour ensures that a value being packed and then unpacked would not change. However, if the value is a string, the stringified version of the string (i.e. wrapped in "") is put inside the store.

The packing and unpacking behaviours can be customised at general level or at individual property level. An unpacker at individual level can also act as an initializer, to provide a default value where no value is provided in props.settings.

When using Typescript the wrapper uses a generic type variable to denote the setting's type, allowing the development tools to type checking and autocomplete the unpacked settings.


See below. The code examples are provided in Typescript and TSX.

Install the library

npm i --save fitbit-settings-commons

Import the artifacts

import {TypedSettingProps, ASIS, SettingsComponentProps, StringifyParseOptions} from "fitbit-settings-commons"

See API document for details.

Using TypedSettingProps Wrapper

To use TypedSettingProps in typescript, it's preferrable to first define the settings type, for example:

interface SettingType {
  stringVal?: string ;
  stringConfusingVal_s?: string ;
  numberVal?: number;
    | {
    | undefined;
  arrayVal?: string[] | undefined;

Then, at the begining of the Settings JSX, wrap the received props parameter with a new TypedSettingProps object. Later codes can then work with this wrapper instead of the props object directly.

const typedSetting : TypedSettingProps<SettingType>
    = new TypedSettingProps(props);

Accessing the unpacked setting values

The get() method of the wrapper returns the unpacked settings. For example:

    const stringProperty = typedSetting.get().objVal?.stringProp;
    const arrayElement = typedSetting.get().arrayVal![1];

Updating a setting by putting a new value

Use update() method to put new setting values or replace existing values. It receives an object as parameter, copies all enumerable own properties of the object to the unpacked settings (similar to Object.assign()), and persists the changes to props.settingsStorage behind the scene.

For example:

      stringVal:"new string val"

If SettingsType generic type is provided, the parameter of the update() method is typed. In typescript, type checking and autocomplete will be available to the parameter.

      stringVal: 42 // error

Updating part of a setting object or array

If an existing setting value is an object or array, to update part of the value without replacing the whole object or array, use getToUpdate(). This method returns a tracked setting object. When accessing a property of the tracked setting object through a key, the key is marked as 'dirty', meaning it's assumed that the property is changed and needs to be persisted to settingsStorage later. In the end the commit() method of the wrapper needs to be called to persist all the 'dirty' properties. For example:

    typedSetting.getToUpdate().objVal!.stringProp = 'new property';
    typedSetting.getToUpdate().arrayVal!.push('new element');

The returned tracked setting object is typed and readonly. Any property such as an object or array can be partially updated but not replaced. To set a property directly, use update().

Updating a setting ASIS

Another way of updating settings is to make the changes directly on the unpacked settings, then call update() with a constant ASIS, which is exported from this library as a marker to denote the changed properties. The value of the denoted property would be taken from the unpacked settings "as is".

For example, after partially changing the property objVal, the two callings of update() are equal, however using ASIS makes the method 1 shorter and less prone to error.

    typedSetting.get().objVal!.stringProp = "new string";
    // method 1
      objVal: ASIS
    // method 2
      objVal: typedSetting.get().objVal

Set Stringify Parse Behaviour

The constructor of the wrapper TypedSettingProps can receive two additional optional parameters to customise the packing / unpacking / initialisation behaviour of the wrapper for individual setting keys as well as the default behaviour for all keys.

    private propsSettingsComponentProps,
    private packerUnpackers?: PackerUnpackerOption<SettingsType>,
    defaultPackerUnpacker?: DefaultPackerUnpackerOption

The parameter packerUnpackers customise wrapper's packing / unpacking / initialization behaviour for individual properties of the settings. The value should be an object with matching keys of the SettingsType. Under a matching key, 'packer' and 'unpackInitiator' can optionally be provided as functions. For example:

      packerv => v,
      unpackInitiatorv => v
  • A packer function receives a value of the type of the matching SettingsType property and returns a string.
  • An unpackInitiator receives a string or undefined and returns a value of the type of the matching SettingsType property. If an unpackInitiator is provided, but no setting is under the matching key in props.settings, the unpackInitiator will be called with undefined, acting as an initiator to return a default value for the key.

The parameter defaultPackerUnpacker customise the default pack / unpack behaviour of the wrapper for all SettingsType properties. The value should be an object, with optional keys packer and / or unpacker providing the default packer / unpacker. Example value below sets a behaviour identical to the default behaviour of the wrapper.


Extending type checking to "settingsKey" in settings components

Fitbit settings components, such as <TextInput>, accepts a settingsKey property that specifies where in the settings storage to put the input value. Without type checking, you can give it any string.

If you are already using fitbit-sdk-types (, then you can extend type checking to the "settingsKey" in the components. To use this feature, first follow the steps in fitbit-sdk-types package's README and make sure it's properly set up. Then replace the 'fitbit-sdk-types' package with a patched version:

npm i --save-dev github:bingtimren/fitbit-sdk-types#release

Now the components can accept a SettingsType type variable, and the settingsKey property would only accept a key in the SettingsType that has a value type matching the type of value that the component will put under that key.

For example, below <Slider> accepts a type variable SliderSettingsType. Since the value <Slider> puts is a number, now settingsKey will only accept numberKey and assignableKey as ligitimate values because other keys does not match the type.

interface SliderSettingsType {
    stringKey: string;
    booleanKey: boolean;
    numberKey: number;
    assignableKey: number | undefined;

See for more usage examples for other components.

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