Added TypeScript Implementation for Armstrong Numbers

Armstrong Numbers/ArmstrongNumbers.ts

@@ -0,0 +1,25 @@
+/**
+ * Function to check whether a given number is an Armstrong Number or not
+ */
+const armstrongNumber = (num: number): boolean => {
+    // Check to see if it meets the conditions
+    if (Number.isNaN(num) || num < 0)
+        return `${num} is not a valid number.`
+
+    const order = num.toString().length;
+    let temp = num;
+    let sum = 0;
+    while (temp) {
+        let digit = temp % 10;
+        sum += Math.pow(digit, order);
+        temp = Math.floor(temp / 10);
+    }
+
+    return (sum === num);
+}
+
+// Sample driver code
+/*
+INPUT:  console.log(armstrongNumber(153));
+OUTPUT: true
+*/