How to update existing object value on storage

Hi,
i’m using angular 2 storage, i want to update existing object value but i can’t update.

i’m using below methods
//for get compaint
getCompaintData() {
return this.storage.get(‘compaint’);
}
//save compaint
saveCompaintData(data){
let newData = JSON.stringify(data);
this.storage.set(‘compaint’, newData);
}
//update complaint data
// data include object

updateCompaintData(data){
let returnStatus:boolean = false;
this.storage.get(‘compaint’).then((complaintsDatas) => {
if (complaintsDatas) {
let complaints = JSON.parse(complaintsDatas);
for(let i=0; i < complaints.length;i++){
if(complaints[i].id == data.id){
console.log(‘append’,data.resolveComment);
complaints[i].resolveComment = data.resolveComment;
returnStatus = true;
let newData = JSON.stringify(complaints);
this.storage.set(‘compaint’, newData);
}
}
}
});
return returnStatus;
}

for example my
ComplaintData =
{“id”:1,“name”:“Bhumin”,“email”:“bhumin@3i”,“companyName”:“3i-info”,“mobileNo”:“90231221212”,“complaintRegarding”:“company name rergister”,“complaintText”:“company name is going to be change”,“isResolve”:false,“resolveComment”:"",“addDate”:“2017-03-21T06:27:51.326Z”},{“id”:2,“name”:“Manjoj”,“email”:“manoj@3i”,“companyName”:“3i-info”,“mobileNo”:“98908909898”,“complaintRegarding”:“comapny name register”,“complaintText”:“want to change company name”,“isResolve”:false,“resolveComment”:"",“addDate”:“2017-03-21T06:30:21.341Z”}

i want to update resolveComment of row 0 but i can’t update it how do they do it?