types: enforce consistent type checking

src/types.js

@@ -0,0 +1,38 @@
+module.exports = function enforce(type, value) {
+  switch (type) {
+    // http://jsperf.com/array-typecheck-2
+    case 'Array': {
+      if (value != null && value.constructor === Array) return
+      break
+    }
+
+    // http://jsperf.com/boolean-typecheck
+    case 'Boolean': {
+      if (typeof value === 'boolean') return
+      break
+    }
+
+    case 'Buffer': {
+      if (Buffer.isBuffer(value)) return
+      break
+    }
+
+    // http://jsperf.com/number-constructor-v-isnan
+    case 'Number': {
+      if (typeof value === 'number') return
+      break
+    }
+
+    // http://jsperf.com/string-typecheck-2
+    case 'String': {
+      if (value != null && value.constructor === String) return
+      break
+    }
+
+    default: {
+      if (value instanceof type) return
+    }
+  }
+
+  throw new TypeError('Expected ' + (type.name || type) + ', got ' + value)
+}