refactoring and better error

src/asyncChain.js

@@ -10,15 +10,17 @@
  */
 export const asyncChain = async (input, ...functions) => {
   try {
-    const [nextFunction] = functions;
+    const [nextFunction, ...nextFunctions] = functions;
     const nextValue = await nextFunction(input);
 
     if (functions.length === 1) {
       return nextValue;
     }
 
-    return await asyncChain(nextValue, ...functions.slice(1));
+    return await asyncChain(nextValue, ...nextFunctions);
   } catch (error) {
-    throw `Failed to chain ${functions} with input ${input}. ERROR: ${error.message}`;
+    throw new Error(`Failed to chain ${functions} with input ${input}.`, {
+      cause: error,
+    });
   }
 };

src/containsAsyncFunction.js

@@ -1,6 +1,2 @@
-// Check if an array of functions contains an async function
-
-const filter = (func) => func.constructor.name === "AsyncFunction";
-
 export const containsAsyncFunction = (functions) =>
-  functions.filter(filter).length > 0;
+  functions.map((fn) => fn.constructor.name === "AsyncFunction").includes(true);

src/index.js

@@ -8,15 +8,13 @@ export const chain = (...parameters) => {
     return null;
   }
 
-  const [nextValue] = parameters;
+  const [nextValue, ...functions] = parameters;
   if (parameters.length === 1) {
     return nextValue;
   }
 
-  const functions = parameters.slice(1);
-
   if (!validFunctions(functions)) {
-    throw new Error(`Invalid function argument.`);
+    throw new Error("Invalid function argument.");
   }
 
   if (containsAsyncFunction(functions)) {

src/syncChain.js

@@ -10,15 +10,17 @@
  */
 export const syncChain = (input, ...functions) => {
   try {
-    const [nextFunction] = functions;
+    const [nextFunction, ...nextFunctions] = functions;
     const nextValue = nextFunction(input);
 
     if (functions.length === 1) {
       return nextValue;
     }
 
-    return syncChain(nextValue, ...functions.slice(1));
+    return syncChain(nextValue, ...nextFunctions);
   } catch (error) {
-    throw `Failed to chain ${functions} with input ${input}. ERROR: ${error.message}`;
+    throw new Error(`Failed to chain ${functions} with input ${input}.`, {
+      cause: error,
+    });
   }
 };

src/validFunctions.js

@@ -2,14 +2,5 @@
  * Check if the input is an array containing functions
  * @param {*} functions
  */
-export const validFunctions = (functions) => {
-  const allAreFunctions = functions
-    .map((fn) => (typeof fn === "function" ? 1 : 0))
-    .reduce((sum, value) => sum * value, 1);
-
-  if (allAreFunctions === 0) {
-    return false;
-  }
-
-  return true;
-};
+export const validFunctions = (functions) =>
+  !functions.map((fn) => typeof fn === "function").includes(false);