add completed interpreter.js

interpreter.js

@@ -0,0 +1,50 @@
+class Calculator {
+    result;
+    expression;
+
+    /*
+     Perform a calculation.
+
+     @param {string} expr the expression to solve
+     @return {Object} the result
+     */
+    calculate(expr) {
+        try {
+            this.result = eval(expr);
+        } catch(err) {
+            alert(err);
+        };
+    };
+
+    interactive() {
+        while (true) {
+            this.input = ``;
+
+            this.input = (this.result != null) ? prompt(this.result) : prompt();
+
+            // Determine whether the user typed a value.
+            if ((this.input) ? this.input.trim() : false) {
+                this.expression = this.input.trim();
+                delete this.input;
+
+                // Solve the expression.
+                this.calculate(this.expression);
+            } else {
+                break;
+            }
+        }
+    }
+
+    constructor() {
+    };
+};
+
+
+function main() {
+    let INSTANCE = new Calculator();
+    INSTANCE.interactive();
+};
+
+main();
+
+