execute command for math and logic calculations

js/commands.js

@@ -6,3 +6,23 @@ function cmd_clear() {
     window.location.reload();
     return "";
 }
+
+function cmd_exec(input) {
+    if (input === undefined)
+        return "You must enter parameters!";
+    const str = input.join(' ');
+    if (/[',:;a-zA-Z]/.test(str) || str === "")
+        return "Invalid input!";
+    const chars = str.split('').filter(e => {
+        const code = e.charCodeAt(0);
+        const s = code ===  32;
+        const a = code >    36;
+        const b = code <    63;
+        const c = code ===  94;
+        const d = code === 124;
+        return !(s || a && b || c || d);
+    });
+    if (chars.length > 0)
+        return "Invalid input!";
+    return (new Function(`return ${str}`))();
+}