Repository: tkh44/emotion (js)
Issue: Dynamic composes values based on props
I want to support choosing what to compose with based on props.

```javascript
const Alert = styled('div')`
  composes: ${props => types[props.type]};
  padding: 10px;
`
```

Pull request description: Allow composes based on props
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Closes #90


Patch:
diff --git a/src/react.js b/src/react.js
index 888241f0..3975bdf2 100644
--- a/src/react.js
+++ b/src/react.js
@@ -11,7 +11,7 @@ export default function (tag, cls, vars = [], content) {
   function Styled (props) {
     const getValue = v => (v && typeof v === 'function' ? v.cls || v(props) : v)
     const className = css(
-      cls,
+      cls.map(getValue),
       vars.map(getValue),
       content
     )


Test patch:
diff --git a/test/__snapshots__/react.test.js.snap b/test/__snapshots__/react.test.js.snap
index bfa1ecb5..ca1de879 100644
--- a/test/__snapshots__/react.test.js.snap
+++ b/test/__snapshots__/react.test.js.snap
@@ -92,6 +92,35 @@ exports[`styled composes 1`] = `
 </h1>
 `;
 
+exports[`styled composes based on props 1`] = `
+.css-cssA-cy897j-1p4ppuj {
+  color: blue;
+}
+
+
+
+<h1
+  a={true}
+  className="css-H1-16dw226-196nx3w css-H1-16dw226 css-cssA-cy897j-1p4ppuj css-cssA-cy897j"
+>
+  hello world
+</h1>
+`;
+
+exports[`styled composes based on props 2`] = `
+.css-cssB-7o6h5j-dcpp5a {
+  color: green;
+}
+
+
+
+<h1
+  className="css-H1-16dw226-196nx3w css-H1-16dw226 css-cssB-7o6h5j-dcpp5a css-cssB-7o6h5j"
+>
+  hello world
+</h1>
+`;
+
 exports[`styled composes with objects 1`] = `
 .css-cssB-ob3sm8-fwh0v {
   height: 64px;
diff --git a/test/react.test.js b/test/react.test.js
index 27a3c824..7610d5e7 100644
--- a/test/react.test.js
+++ b/test/react.test.js
@@ -232,6 +232,39 @@ describe('styled', () => {
 
     expect(tree).toMatchSnapshotWithEmotion()
   })
+
+  test('composes based on props', () => {
+    const cssA = css`
+      color: blue;
+    `
+
+    const cssB = css`
+      color: green;
+    `
+
+    const H1 = styled('h1')`
+      composes: ${props => props.a ? cssA : cssB}
+    `
+
+    const tree = renderer
+      .create(
+        <H1 a>
+          hello world
+        </H1>
+      )
+      .toJSON()
+
+    expect(tree).toMatchSnapshotWithEmotion()
+    const tree2 = renderer
+      .create(
+        <H1>
+          hello world
+        </H1>
+      )
+      .toJSON()
+
+    expect(tree2).toMatchSnapshotWithEmotion()
+  })
   test('throws if undefined is passed as the component', () => {
     expect(
       () => styled(undefined)`display: flex;`