Swaps in arrays

Given a string 'S' swap the even and odd characters starting from index 1(Assume the index starts from 0).
Input Size : |s| <= 10000000(complexity O(n))
Sample Testcase :
INPUT
codekata
OUTPUT
ocedakat

test.js

@@ -0,0 +1,29 @@
+
+// Getting input via STDIN
+const readline = require("readline");
+
+const inp = readline.createInterface({
+  input: process.stdin
+});
+
+const userInput = [];
+
+inp.on("line", (data) => {
+  userInput.push(data);
+});
+
+inp.on("close", () => {
+    let a=userInput[0].split("");
+    let temp=0;
+  for( var i=0;i<a.length;i++){
+      if(i%2 === 0){
+          if(i+1<a.length){
+             temp=a[i];
+            a[i]=a[i+1];
+             a[i+1]=temp;} 
+          }
+      }
+
+  a=a.join(" ")
+  console.log(a);
+});