feat(length): Add module length

Returns the length of an array or arity of a function

src/__tests__/length.js

@@ -0,0 +1,7 @@
+import length from '../length';
+
+test('Core.length', () => {
+  expect(length([])).toBe(0);
+  expect(length([1, 2, 3])).toBe(3);
+  expect(length((a, b) => a + b)).toBe(2);
+});

src/curry.js

@@ -1,8 +1,10 @@
+import length from './length';
+
 export default fn => {
-  const totalArgs = fn.length;
+  const totalArgs = length(fn);
 
   const curried = (...partialArgs) => (...args) => {
-    if (partialArgs.length + args.length >= totalArgs)
+    if (length(partialArgs) + length(args) >= totalArgs)
       return fn(...partialArgs, ...args);
 
     return curried(...partialArgs, ...args);

src/findIndex.js

@@ -1,6 +1,8 @@
+import length from './length';
+
 export default (predicateFn, arr) => {
   let i = 0;
-  const len = arr.length;
+  const len = length(arr);
 
   while (i < len) {
     const val = arr[i];

src/index.js

@@ -17,6 +17,7 @@ import isObject from './isObject';
 import isString from './isString';
 import join from './join';
 import last from './last';
+import length from './length';
 import map from './map';
 import nth from './nth';
 import pipe from './pipe';
@@ -46,6 +47,7 @@ export {
   isString,
   join,
   last,
+  length,
   map,
   nth,
   pipe,

src/length.js

@@ -0,0 +1 @@
+export default arr => arr.length;

src/nth.js

@@ -1,4 +1,6 @@
+import length from './length';
+
 export default (n, arr) => {
-  const index = n < 0 ? arr.length + n : n;
+  const index = n < 0 ? length(arr) + n : n;
   return typeof arr === 'string' ? arr.charAt(index) : arr[index];
 };

src/reduce.js

@@ -1,5 +1,7 @@
+import length from './length';
+
 export default (fn, init, arr) => {
   let l = init;
-  for (let i = 0; i < arr.length; i++) l = fn(l, arr[i]);
+  for (let i = 0; i < length(arr); i++) l = fn(l, arr[i]);
   return l;
 };

src/reduceRight.js

@@ -1,5 +1,7 @@
+import length from './length';
+
 export default (fn, init, arr) => {
   let l = init;
-  for (let i = arr.length - 1; i >= 0; i--) l = fn(l, arr[i]);
+  for (let i = length(arr) - 1; i >= 0; i--) l = fn(l, arr[i]);
   return l;
 };