[improvement] rename packages dir to src (#3659)

src/utils/create/bem.ts

@@ -0,0 +1,49 @@
+/**
+ * bem helper
+ * b() // 'button'
+ * b('text') // 'button__text'
+ * b({ disabled }) // 'button button--disabled'
+ * b('text', { disabled }) // 'button__text button__text--disabled'
+ * b(['disabled', 'primary']) // 'button button--disabled button--primary'
+ */
+
+export type Mod = string | { [key: string]: any };
+export type Mods = Mod | Mod[];
+
+const ELEMENT = '__';
+const MODS = '--';
+
+function join(name: string, el?: string, symbol?: string): string {
+  return el ? name + symbol + el : name;
+}
+
+function prefix(name: string, mods: Mods): Mods {
+  if (typeof mods === 'string') {
+    return join(name, mods, MODS);
+  }
+
+  if (Array.isArray(mods)) {
+    return mods.map(item => <Mod>prefix(name, item));
+  }
+
+  const ret: Mods = {};
+  if (mods) {
+    Object.keys(mods).forEach(key => {
+      ret[name + MODS + key] = mods[key];
+    });
+  }
+
+  return ret;
+}
+
+export function createBEM(name: string) {
+  return function (el?: Mods, mods?: Mods): Mods {
+    if (el && typeof el !== 'string') {
+      mods = el;
+      el = '';
+    }
+    el = join(name, el, ELEMENT);
+
+    return mods ? [el, prefix(el, mods)] : el;
+  };
+}