LibJS: Implement basic support for the "delete" operator

It turns out "delete" is actually a unary op :)
This patch implements deletion of object properties, it doesn't yet
work for casually deleting properties from the global object.

When deleting a property from an object, we switch that object to
having a unique shape, no longer sharing shapes with others.
Once an object has a unique shape, it no longer needs to care about
shape transitions.

1 files changed, 60 insertions, 0 deletions

diff --git a/Libraries/LibJS/Tests/delete-basic.js b/Libraries/LibJS/Tests/delete-basic.js
new file mode 100644
index 0000000000..eda9741b6b
--- /dev/null
+++ b/Libraries/LibJS/Tests/delete-basic.js
@@ -0,0 +1,60 @@
+load("test-common.js");
+
+try {
+    o = {};
+    o.x = 1;
+    o.y = 2;
+    o.z = 3;
+    assert(Object.getOwnPropertyNames(o).length === 3);
+
+    assert(delete o.x === true);
+    assert(o.hasOwnProperty('x') === false);
+    assert(o.hasOwnProperty('y') === true);
+    assert(o.hasOwnProperty('z') === true);
+    assert(Object.getOwnPropertyNames(o).length === 2);
+
+    assert(delete o.y === true);
+    assert(o.hasOwnProperty('x') === false);
+    assert(o.hasOwnProperty('y') === false);
+    assert(o.hasOwnProperty('z') === true);
+    assert(Object.getOwnPropertyNames(o).length === 1);
+
+    assert(delete o.z === true);
+    assert(o.hasOwnProperty('x') === false);
+    assert(o.hasOwnProperty('y') === false);
+    assert(o.hasOwnProperty('z') === false);
+    assert(Object.getOwnPropertyNames(o).length === 0);
+
+    a = [ 3, 5, 7 ];
+
+    assert(Object.getOwnPropertyNames(a).length === 4);
+
+    assert(delete a[0] === true);
+    assert(a.hasOwnProperty(0) === false);
+    assert(a.hasOwnProperty(1) === true);
+    assert(a.hasOwnProperty(2) === true);
+    assert(Object.getOwnPropertyNames(a).length === 3);
+
+    assert(delete a[1] === true);
+    assert(a.hasOwnProperty(0) === false);
+    assert(a.hasOwnProperty(1) === false);
+    assert(a.hasOwnProperty(2) === true);
+    assert(Object.getOwnPropertyNames(a).length === 2);
+
+    assert(delete a[2] === true);
+    assert(a.hasOwnProperty(0) === false);
+    assert(a.hasOwnProperty(1) === false);
+    assert(a.hasOwnProperty(2) === false);
+    assert(Object.getOwnPropertyNames(a).length === 1);
+
+    q = {};
+    Object.defineProperty(q, "foo", { value: 1, writable: false, enumerable: false });
+    assert(q.foo === 1);
+
+    assert(delete q.foo === false);
+    assert(q.hasOwnProperty('foo') === true);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}