fix #9125 (#16582)

* fix #9125

* Update tests/stdlib/tmath.nim

Co-authored-by: Timothee Cour <timothee.cour2@gmail.com>

* back

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>
Co-authored-by: Timothee Cour <timothee.cour2@gmail.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/lib/pure/math.nim b/lib/pure/math.nim
index 76052ec3b..a6a3676b9 100644
--- a/lib/pure/math.nim
+++ b/lib/pure/math.nim
@@ -847,7 +847,17 @@ else: # JS
   func floor*(x: float64): float64 {.importc: "Math.floor", nodecl.}
   func ceil*(x: float32): float32 {.importc: "Math.ceil", nodecl.}
   func ceil*(x: float64): float64 {.importc: "Math.ceil", nodecl.}
-  func round*(x: float): float {.importc: "Math.round", nodecl.}
+
+  when (NimMajor, NimMinor) < (1, 5) or defined(nimLegacyJsRound):
+    func round*(x: float): float {.importc: "Math.round", nodecl.}
+  else:
+    func jsRound(x: float): float {.importc: "Math.round", nodecl.}
+    func round*[T: float64 | float32](x: T): T =
+      if x >= 0: result = jsRound(x)
+      else:
+        result = ceil(x)
+        if result - x >= T(0.5):
+          result -= T(1.0)
   func trunc*(x: float32): float32 {.importc: "Math.trunc", nodecl.}
   func trunc*(x: float64): float64 {.importc: "Math.trunc", nodecl.}