NativeScript/tns-core-modules/application-settings/application-settings-common.ts

export var checkKey = function (key: string): void {
    if (typeof key !== "string") {
        throw new Error("key: '" + key + "' must be a string");
    }
}

export var ensureValidValue = function (value: any, valueType: string): void {
    if (typeof value !== valueType) {
        throw new Error("value: '" + value + "' must be a " + valueType);
    }
}