LibJS: Add JSON.stringify

Libraries/LibJS/Tests/JSON.stringify-replacer.js

@@ -0,0 +1,39 @@
+load("test-common.js");
+
+try {
+    let o = {
+        var1: "foo",
+        var2: 42,
+        arr: [1, 2, {
+            nested: {
+                hello: "world",
+            },
+            get x() { return 10; }
+        }],
+        obj: {
+            subarr: [3],
+        },
+    };
+
+    let string = JSON.stringify(o, (key, value) => {
+        if (key === "hello")
+            return undefined;
+        if (value === 10)
+            return 20;
+        if (key === "subarr")
+            return [3, 4, 5];
+        return value;
+    });
+
+    assert(string === '{"var1":"foo","var2":42,"arr":[1,2,{"nested":{},"x":20}],"obj":{"subarr":[3,4,5]}}');
+
+    string = JSON.stringify(o, ["var1", "var1", "var2", "obj"]);
+    assert(string == '{"var1":"foo","var2":42,"obj":{}}');
+
+    string = JSON.stringify(o, ["var1", "var1", "var2", "obj", "subarr"]);
+    assert(string == '{"var1":"foo","var2":42,"obj":{"subarr":[3]}}');
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}