Add fr.cx

Author: garronej

src/lib/cx.ts

@@ -0,0 +1,54 @@
+import { assert } from "tsafe/assert";
+import { typeGuard } from "tsafe/typeGuard";
+import type { FrClassName } from "./generatedFromCss/classNames";
+
+export type FrCxArg =
+    | undefined
+    | null
+    | FrClassName
+    | boolean
+    | Partial<Record<FrClassName, boolean | null | undefined>>
+    | readonly FrCxArg[];
+
+/** Copy pasted from
+ * https://github.com/emotion-js/emotion/blob/23f43ab9f24d44219b0b007a00f4ac681fe8712e/packages/react/src/class-names.js#L17-L63
+ **/
+export const cx = (args: FrCxArg[]): string => {
+    const len = args.length;
+    let i = 0;
+    let cls = "";
+    for (; i < len; i++) {
+        const arg = args[i];
+        if (arg == null) continue;
+
+        let toAdd;
+        switch (typeof arg) {
+            case "boolean":
+                break;
+            case "object": {
+                if (Array.isArray(arg)) {
+                    toAdd = cx(arg);
+                } else {
+                    assert(!typeGuard<{ length: number }>(arg, false));
+
+                    toAdd = "";
+                    for (const k in arg) {
+                        if (arg[k as FrClassName] && k) {
+                            toAdd && (toAdd += " ");
+                            toAdd += k;
+                        }
+                    }
+                }
+                break;
+            }
+            default: {
+                toAdd = arg;
+            }
+        }
+        if (toAdd) {
+            cls && (cls += " ");
+            cls += toAdd;
+        }
+    }
+    return cls;
+};

src/lib/index.ts

@@ -5,8 +5,11 @@ export type { BreakpointKeys } from "./breakpoints";
 import { breakpoints } from "./breakpoints";
 import { spacing } from "./spacing";
 export type { SpacingToken } from "./spacing";
+import { cx } from "./cx";
+export type { FrCxArg } from "./cx";
 
 export const fr = {
     breakpoints,
-    spacing
+    spacing,
+    cx
 };