[improvement] memoize bem (#1054)

packages/wxs/memoize.wxs

@@ -0,0 +1,52 @@
+/**
+ * Simple memoize
+ * wxs doesn't support fn.apply, so this memoize only support up to 2 args
+ */
+
+function isPrimitive(value) {
+  var type = typeof value;
+  return (
+    type === 'boolean' ||
+    type === 'number' ||
+    type === 'string' ||
+    type === 'undefined' ||
+    value === null
+  );
+}
+
+// mock simple fn.call in wxs
+function call(fn, args) {
+  if (args.length === 2) {
+    return fn(args[0], args[1]);
+  }
+
+  if (args.length === 1) {
+    return fn(args[0]);
+  }
+
+  return fn();
+}
+
+function serializer(args) {
+  if (args.length === 1 && isPrimitive(args[0])) {
+    return args[0];
+  }
+
+  return JSON.stringify(args.length === 1 ? args[0] : args);
+}
+
+function memoize(fn) {
+  var cache = {};
+
+  return function() {
+    var key = serializer(arguments);
+
+    if (cache[key] === undefined) {
+      cache[key] = call(fn, arguments);
+    }
+
+    return cache[key];
+  };
+}
+
+module.exports.memoize = memoize;

packages/wxs/utils.wxs

@@ -1,8 +1,12 @@
 var bem = require('./bem.wxs').bem;
+var memoize = require('./memoize.wxs').memoize;
 
 function isSrc(url) {
   return url.indexOf('http') === 0 || url.indexOf('data:image') === 0;
 }
 
-module.exports.bem = bem;
-module.exports.isSrc = isSrc;
+module.exports = {
+  bem: memoize(bem),
+  isSrc: isSrc,
+  memoize: memoize
+};