feat(compose): this and args passed to first function

@vates/compose/README.md

@@ -29,6 +29,19 @@ console.log(f(5))
 // → 21
 ```
 
+The first function is called with the context and all arguments of the composed function:
+
+```js
+const add = (x, y) => x + y
+const mul3 = x => x * 3
+
+// const f = (x, y) => mul3(add(x, y))
+const f = compose(add, mul3)
+
+console.log(f(4, 5))
+// → 27
+```
+
 Functions may also be passed in an array:
 
 ```js

@vates/compose/USAGE.md

@@ -11,6 +11,19 @@ console.log(f(5))
 // → 21
 ```
 
+The first function is called with the context and all arguments of the composed function:
+
+```js
+const add = (x, y) => x + y
+const mul3 = x => x * 3
+
+// const f = (x, y) => mul3(add(x, y))
+const f = compose(add, mul3)
+
+console.log(f(4, 5))
+// → 27
+```
+
 Functions may also be passed in an array:
 
 ```js

@vates/compose/index.js

@@ -29,14 +29,16 @@ exports.compose = function compose(opts, fns) {
   }
 
   return opts.async
-    ? async function (value) {
-        for (let i = 0; i < n; ++i) {
+    ? async function () {
+        let value = await fns[0].apply(this, arguments)
+        for (let i = 1; i < n; ++i) {
           value = await fns[i](value)
         }
         return value
       }
-    : function (value) {
-        for (let i = 0; i < n; ++i) {
+    : function () {
+        let value = fns[0].apply(this, arguments)
+        for (let i = 1; i < n; ++i) {
           value = fns[i](value)
         }
         return value

@vates/compose/index.spec.js

@@ -36,4 +36,19 @@ describe('compose()', () => {
       )(5)
     ).toBe(21)
   })
+
+  it('first function receives this and all args', () => {
+    expect.assertions(2)
+
+    const expectedArgs = [Math.random(), Math.random()]
+    const expectedThis = {}
+    compose(
+      function (...args) {
+        expect(this).toBe(expectedThis)
+        expect(args).toEqual(expectedArgs)
+      },
+      // add a second function to use the one function special case
+      Function.prototype
+    ).apply(expectedThis, expectedArgs)
+  })
 })