LibJS: Add parsing and evaluation of private fields and methods

Userland/Libraries/LibJS/Tests/classes/class-private-fields.js

@@ -0,0 +1,88 @@
+test("basic functionality", () => {
+    class A {
+        #number = 3;
+
+        getNumber() {
+            return this.#number;
+        }
+
+        #string = "foo";
+
+        getString() {
+            return this.#string;
+        }
+
+        #uninitialized;
+
+        getUninitialized() {
+            return this.#uninitialized;
+        }
+    }
+
+    const a = new A();
+    expect(a.getNumber()).toBe(3);
+    expect(a.getString()).toBe("foo");
+    expect(a.getUninitialized()).toBeUndefined();
+
+    expect("a.#number").not.toEval();
+    expect("a.#string").not.toEval();
+    expect("a.#uninitialized").not.toEval();
+});
+
+test("initializer has correct this value", () => {
+    class A {
+        #thisVal = this;
+
+        getThisVal() {
+            return this.#thisVal;
+        }
+
+        #thisName = this.#thisVal;
+
+        getThisName() {
+            return this.#thisName;
+        }
+    }
+
+    const a = new A();
+    expect(a.getThisVal()).toBe(a);
+    expect(a.getThisName()).toBe(a);
+});
+
+test("static fields", () => {
+    class A {
+        static #simple = 1;
+
+        static getStaticSimple() {
+            return this.#simple;
+        }
+
+        static #thisVal = this;
+        static #thisName = this.name;
+        static #thisVal2 = this.#thisVal;
+
+        static getThisVal() {
+            return this.#thisVal;
+        }
+
+        static getThisName() {
+            return this.#thisName;
+        }
+
+        static getThisVal2() {
+            return this.#thisVal2;
+        }
+    }
+
+    expect(A.getStaticSimple()).toBe(1);
+
+    expect(A.getThisVal()).toBe(A);
+    expect(A.getThisName()).toBe("A");
+    expect(A.getThisVal2()).toBe(A);
+
+    expect("A.#simple").not.toEval();
+});
+
+test("cannot have static and non static field with the same description", () => {
+    expect("class A { static #simple; #simple; }").not.toEval();
+});