CLJS-1784 - nth doesn't throw on strings or arrays

nth now throws on arrays and strings when n is out of bounds.

Author: thomasmulvaney

src/main/cljs/cljs/core.cljs

@@ -1742,7 +1742,7 @@ reduces them without incurring seq initialization"
   ([coll n]
     (cond
       (not (number? n))
-      (throw (js/Error. "index argument to nth must be a number"))
+      (throw (js/Error. "Index argument to nth must be a number"))
 
       (nil? coll)
       coll
@@ -1751,12 +1751,14 @@ reduces them without incurring seq initialization"
       (-nth ^not-native coll n)
 
       (array? coll)
-      (when (< n (.-length coll))
-        (aget coll n))
+      (if (and (>= n 0) (< n (.-length coll)))
+        (aget coll n)
+        (throw (js/Error. "Index out of bounds")))
 
       (string? coll)
-      (when (< n (.-length coll))
-        (.charAt coll n))
+      (if (and (>= n 0) (< n (.-length coll)))
+        (.charAt coll n)
+        (throw (js/Error. "Index out of bounds")))
 
       (implements? ISeq coll)
       (linear-traversal-nth coll n)
@@ -1770,7 +1772,7 @@ reduces them without incurring seq initialization"
   ([coll n not-found]
     (cond
       (not (number? n))
-      (throw (js/Error. "index argument to nth must be a number."))
+      (throw (js/Error. "Index argument to nth must be a number."))
 
       (nil? coll)
       not-found
@@ -1779,12 +1781,12 @@ reduces them without incurring seq initialization"
       (-nth ^not-native coll n not-found)
 
       (array? coll)
-      (if (< n (.-length coll))
+      (if (and (>= n 0) (< n (.-length coll)))
         (aget coll n)
         not-found)
 
       (string? coll)
-      (if (< n (.-length coll))
+      (if (and (>= n 0) (< n (.-length coll)))
         (.charAt coll n)
         not-found)
 

src/test/cljs/cljs/core_test.cljs

@@ -3293,6 +3293,17 @@
     (is (= (foo-fn foo {:a 1 :b 2})
            {:c 3}))))
 
+(deftest test-cljs-1748
+  (is (thrown? js/Error (nth (array 0 1 2)  3)))
+  (is (thrown? js/Error (nth (array 0 1 2) -1)))
+  (is (= (nth (array 0 1 2)  3 :not-found) :not-found))
+  (is (= (nth (array 0 1 2) -1 :not-found) :not-found))
+
+  (is (thrown? js/Error (nth "012"  3)))
+  (is (thrown? js/Error (nth "012" -1)))
+  (is (= (nth "012"  3 :not-found) :not-found))
+  (is (= (nth "012" -1 :not-found) :not-found)))
+
 (comment
   ;; ObjMap
   ;; (let [ks (map (partial str "foo") (range 500))