Add delete operator example

Closes: #5

JavaScript/7-delete.js

@@ -0,0 +1,31 @@
+'use strict';
+
+const org = 'HowProgrammingWorks';
+
+// delete org; // Raises SyntaxError in strict mode
+
+const country = {
+  name: 'Chile',
+  ruler: 'Augusto Pinochet',
+  born: 1915,
+  alive: false
+};
+
+delete country.ruler;
+console.dir({ country });
+
+delete country.born;
+delete country.population;
+console.dir({ country });
+
+const currencies = ['BTC', 'EUR', 'UAH', 'USD'];
+
+console.log('currencies[1]:', currencies[1], 1 in currencies);
+console.log('currencies[2]:', currencies[2], 2 in currencies);
+
+delete currencies[1];
+currencies[2] = undefined;
+console.dir({ currencies });
+
+console.log('currencies[1]:', currencies[1], 1 in currencies);
+console.log('currencies[2]:', currencies[2], 2 in currencies);