JS: backport few echo bugfixes to string.inspect

CHANGELOG.md

@@ -1,5 +1,12 @@
 # Changelog
 
+## Unreleased
+
+- Fixed a bug where `string.inspect` on the JavaScript target would incorrectly
+  print numbers like `1.0e300`.
+- Fixed a bug where `stting.inspect` on the JavaScript target would incorrectly
+  print NaN and Infinity.
+
 ## v1.0.5 - 2026-08-06
 
 - Fixed a bug where `bit_array.pad_to_bytes` could crash.

src/gleam_stdlib.mjs

@@ -702,8 +702,11 @@ export function float_to_string(float) {
     const index = string.indexOf("e");
     if (index >= 0) {
       return string.slice(0, index) + ".0" + string.slice(index);
-    } else {
+    } else if (globalThis.Number.isInteger(float)) {
       return string + ".0";
+    } else {
+      // For NaN and Infinity we return it as JS representation.
+      return "//js(" + string + ")";
     }
   }
 }
@@ -718,7 +721,7 @@ class Inspector {
     if (v === null) return "//js(null)";
     if (v === undefined) return "Nil";
     if (t === "string") return this.#string(v);
-    if (t === "bigint" || Number.isInteger(v)) return v.toString();
+    if (t === "bigint" || Number.isSafeInteger(v)) return v.toString();
     if (t === "number") return float_to_string(v);
     if (v instanceof UtfCodepoint) return this.#utfCodepoint(v);
     if (v instanceof BitArray) return this.#bit_array(v);

test/gleam/string_test.gleam

@@ -1262,6 +1262,14 @@ pub fn inspect_451_test() {
   assert string.inspect(<<255, 2, 0>>) == "<<255, 2, 0>>"
 }
 
+pub fn inspect_456_test() {
+  assert string.inspect(1.0e300) == "1.0e300"
+}
+
+pub fn inspect_461_test() {
+  assert string.inspect(1.0e-300) == "1.0e-300"
+}
+
 pub fn inspect_charlist_test() {
   let list = [
     70, 97, 105, 108, 101, 100, 32, 116, 111, 32, 108, 111, 97, 100, 32, 78, 73,
@@ -1317,6 +1325,19 @@ pub fn target_inspect_bit_array_test() {
   assert string.inspect(<<"abc":utf8>>) == "<<97, 98, 99>>"
 }
 
+@target(javascript)
+pub fn target_inspect_nan_test() {
+  let infinity = 1.0e300 *. 1.0e300
+  let nan = infinity /. infinity
+  assert string.inspect(nan) == "//js(NaN)"
+}
+
+@target(javascript)
+pub fn target_inspect_infinity_test() {
+  let infinity = 1.0e300 *. 1.0e300
+  assert string.inspect(infinity) == "//js(Infinity)"
+}
+
 @target(erlang)
 @external(erlang, "erlang", "self")
 fn create_erlang_pid() -> String