feat(compose): forwards this to all functions

@vates/compose/USAGE.md

@@ -11,7 +11,9 @@ console.log(f(5))
 // → 21
 ```
 
-The first function is called with the context and all arguments of the composed function:
+> The call context (`this`) of the composed function is forwarded to all functions.
+
+The first function is called with all arguments of the composed function:
 
 ```js
 const add = (x, y) => x + y

@vates/compose/index.js

@@ -32,14 +32,14 @@ exports.compose = function compose(opts, fns) {
     ? async function () {
         let value = await fns[0].apply(this, arguments)
         for (let i = 1; i < n; ++i) {
-          value = await fns[i](value)
+          value = await fns[i].call(this, value)
         }
         return value
       }
     : function () {
         let value = fns[0].apply(this, arguments)
         for (let i = 1; i < n; ++i) {
-          value = fns[i](value)
+          value = fns[i].call(this, value)
         }
         return value
       }

@vates/compose/index.spec.js

@@ -37,18 +37,30 @@ describe('compose()', () => {
     ).toBe(21)
   })
 
-  it('first function receives this and all args', () => {
-    expect.assertions(2)
+  it('forwards all args to first function', () => {
+    expect.assertions(1)
 
     const expectedArgs = [Math.random(), Math.random()]
-    const expectedThis = {}
     compose(
-      function (...args) {
-        expect(this).toBe(expectedThis)
+      (...args) => {
         expect(args).toEqual(expectedArgs)
       },
-      // add a second function to use the one function special case
+      // add a second function to avoid the one function special case
       Function.prototype
-    ).apply(expectedThis, expectedArgs)
+    )(...expectedArgs)
+  })
+
+  it('forwards context to all functions', () => {
+    expect.assertions(2)
+
+    const expectedThis = {}
+    compose(
+      function () {
+        expect(this).toBe(expectedThis)
+      },
+      function () {
+        expect(this).toBe(expectedThis)
+      }
+    ).call(expectedThis)
   })
 })