Fix JavaScript object equality

Closes https://github.com/gleam-lang/gleam/issues/4699

CHANGELOG.md

···
   bit array segment on the JavaScript target.
   ([Surya Rose](https://github.com/GearsDatapacks))
 
+- Fixed a bug where `==` and `!=` would return incorrect output for some
+  JavaScript objects.
+  ([Louis Pilfold](https://github.com/lpil))
+
 ## v1.11.1 - 2025-06-05
 
 ### Compiler

compiler-core/src/javascript.rs

···
     }
 }
 
-fn jsdoc_comment<'a>(documentation: &'a EcoString, publicity: Publicity) -> Document<'a> {
+fn jsdoc_comment(documentation: &EcoString, publicity: Publicity) -> Document<'_> {
     let doc_lines = documentation
         .trim_end()
         .split('\n')

compiler-core/templates/prelude.mjs

···
     }
 
     let [keys, get] = getters(a);
-    for (let k of keys(a)) {
+    const ka = keys(a);
+    const kb = keys(b);
+    if (ka.length !== kb.length) return false;
+    for (let k of ka) {
       values.push(get(a, k), get(b, k));
     }
   }

test/javascript_prelude/main.mjs

···
   new Map([["a", new Map([["a", []]])]]),
 );
 
+assertNotEqual(new Map([]), new Map([["b", 1]]));
+
 // Sets are compared structurally
 let set = new Set(["a", 1]);
 assertEqual(set, set);
···
 // custom equals defined on object instead of prototype, don't use it
 assertEqual(hasEqualsField, { ...hasEqualsField });
 assertNotEqual(hasEqualsField, hasEqualsField2);
+
+// Objects
+assertEqual({ a: 1 }, { a: 1 });
+assertEqual({ a: 1, b: 2 }, { b: 2, a: 1 });
+
+assertEqual({ a: {} }, { a: {} });
+assertEqual({ a: 1, b: { c: 3 } }, { a: 1, b: { c: 3 } });
+
+assertNotEqual({ a: 1 }, {});
+assertNotEqual({ a: 1, b: 2 }, { b: 2 });
+assertNotEqual({}, { a: 1 });
+assertNotEqual({ b: 2 }, { a: 1, b: 2 });
 
 // BitArray