Redis in Nodejs for loop not working properly - node.js

Question

I have a for loop like below which isn't getting executed as expected.
var redis = require('redis');
var client = redis.createClient();
var arr = [{title:"title1"},{title:"title2"},{title:"title3"},{title:"title4"}];
for(var i =0; i<arr.length; i++){
//console.log(arr[i]);
var obj1 = arr[i];
client.get(obj1.title, function(err, response){
if(err){
console.log(err);
}
if(response){
if(i%3==0){
client.del(obj1.title);
}else{
client.incr(obj1.title);
}
}else{
client.set(obj1.title, 1);
}
});
}
The output on running the below code afterwards was
for(var i=0; i<arr.length; i++){
client.get(arr[i].title, redis.print);
}
The output:
Reply: null
Reply: null
Reply: null
Reply: null
Reply: null
Reply: null
Reply: 2
which was not what i expected, since all values except the one divisible by 3 should be atleast 1;

Answer 1

Please create a new function. In the new function, you can delete, increment or creating the new key.
The below code works fine for me. Please check.
var redis = require('redis');
var client = redis.createClient();
var arr = [ {
title : "title1"
}, {
title : "title2"
}, {
title : "title3"
}, {
title : "title4"
} ];
function delOrIncr(obj1, i) {
client.get(obj1.title, function(err, response) {
if (err) {
console.log(err);
}
if (response) {
if (i % 3 === 0) {
console.log('Deleting >' + obj1.title);
client.del(obj1.title);
} else {
console.log('Increment >' + obj1.title);
client.incr(obj1.title);
}
} else {
console.log('Creating new >' + obj1.title);
client.set(obj1.title, 1);
}
});
}
for (var i = 0; i < arr.length; i++) {
delOrIncr(arr[i], i);
}
Note:-
Please run the get as a separate program to check the result of the above program.

Answer 2

var redis = require('redis');
var client = redis.createClient();
var arr = [{title:"title1"},{title:"title2"},{title:"title3"},{title:"title4"}];
for(var i =0; i<arr.length; i++){
//console.log(arr[i]); // this is cool
var obj1 = arr[i];
client.get(obj1.title, function(err, response){
if(err){
console.log(err);
}
if(response){
if(i%3==0){
// mistake 1:
// due to async op,loop will already be over and i will be 3 here
// mistake 2:
// obj1 will be arr[3] here, not what you were expecting :D
client.del(obj1.title);
}else{
client.incr(obj1.title);
}`enter code here`
}else{
// so only the last obj gets stored.
client.set(obj1.title, 1);
}
});
}