Swap order of combinator inputs, fn + args (as in storage) (#537)

* Swap order of combinator inputs, fn + args (as in storage)

* Update api exposed combination

* Update CHANGELOG usage (small doc fix)

CHANGELOG.md

@@ -9,7 +9,7 @@ Tuples now return single types when only one type is available, i.e. `(AccountId
 Api Promise has been updated in the way we deal with subscriptions. Previously a subscription returned `Promise<number>` where the caller was to keep track of the id and use it in subsequent unsubscribes. Now any subscriptions return an unsubscribe/destroy function `(): void`, that is use for removing the subscriptions, e.g.
 
 ```js
-const unsubscribe = api.query.balance.freeBalanceOf(Alice, (balance) => {...});
+const unsubscribe = api.query.balance.freeBalance(Alice, (balance) => {...});
 
 unsubscribe(); // here we destroy the subscription
 ```

packages/api/src/promise/Combinator.ts

@@ -20,12 +20,12 @@ export default class Combinator {
   protected _results: Array<any> = [];
   protected _unsubscriptions: Array<UnsubFunction | any> = [];
 
-  constructor (fns: Array<CombinatorFunction | [Array<any>, CombinatorFunction]>, callback: CombinatorCallback) {
+  constructor (fns: Array<CombinatorFunction | [CombinatorFunction, ...Array<any>]>, callback: CombinatorCallback) {
     this._callback = callback;
     this._unsubscriptions = fns.map((input, index) => {
-      const [args, fn] = Array.isArray(input)
+      const [fn, ...args] = Array.isArray(input)
         ? input
-        : [[], input];
+        : [input];
 
       this._fired.push(false);
       this._fns.push(fn);

packages/api/src/promise/index.ts

@@ -237,15 +237,15 @@ export default class ApiPromise extends ApiBase<DecoratedRpc, QueryableStorage,
    *
    * // combines values from balance & nonce as it updates
    * api.combineLatest([
-   *   (cb) => api.rpc.chain.subscribeNewHead(cb),
-   *   (cb) => api.query.balances.freeBalance(address, cb),
+   *   api.rpc.chain.subscribeNewHead,
+   *   [api.query.balances.freeBalance, address],
    *   (cb) => api.query.system.accountNonce(address, cb)
    * ], ([head, balance, nonce]) => {
    *   console.log(`#${head.number}: You have ${balance} units, with ${nonce} transactions sent`);
    * });
    * ```
    */
-  combineLatest (fns: Array<CombinatorFunction | [Array<any>, CombinatorFunction]>, callback: CombinatorCallback): UnsubFunction {
+  combineLatest (fns: Array<CombinatorFunction | [CombinatorFunction, ...Array<any>]>, callback: CombinatorCallback): UnsubFunction {
     const combinator = new Combinator(fns, callback);
 
     return (): void => {