move misc to js/ui

1-js/99-js-misc/01-proxy/01-error-nonexisting/solution.md

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+
+```js run
+let user = {
+  name: "John"
+};
+
+function wrap(target) {
+  return new Proxy(target, {
+    get(target, prop, receiver) {
+      if (prop in target) {
+        return Reflect.get(target, prop, receiver);
+      } else {
+        throw new ReferenceError(`Property doesn't exist: "${prop}"`)
+      }
+    }
+  });
+}
+
+user = wrap(user);
+
+alert(user.name); // John
+alert(user.age); // Error: Property doesn't exist
+```

1-js/99-js-misc/01-proxy/01-error-nonexisting/task.md

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+
+# Error on reading non-existant property
+
+Create a proxy that throws an error for an attempt to read of a non-existant property.
+
+That can help to detect programming mistakes early.
+
+Write a function `wrap(target)` that takes an object `target` and return a proxy instead with that functionality.
+
+That's how it should work:
+
+```js
+let user = {
+  name: "John"
+};
+
+function wrap(target) {
+  return new Proxy(target, {
+*!*
+      /* your code */
+*/!*
+  });
+}
+
+user = wrap(user);
+
+alert(user.name); // John
+*!*
+alert(user.age); // Error: Property doesn't exist
+*/!*
+```