Search and replace key in array of objects

You could use Array#forEach and check if the key exist.

function replace(oldKey, newKey, array) {
    array.forEach(function (o) {
        if (oldKey in o) {
            o[newKey] = o[oldKey];
            delete o[oldKey];
        }
    });
}

var object = [{ "SerialNumber": '001', "name": "user1" }, { "SerialNumber": '002', "name": "user2" }];
replace('SerialNumber', 'SNo', object);

console.log(object);

It looks as if you switched if and foreach. object is an Array, so you can forEach through items, and there check for your condition.

var object = [
    {
        "SerialNumber": 001,
        "name": "user1"
    },
    {
        "SerialNumber": 002,
        "name": "user2"
    }
];

object.forEach(function (item)  {
    if (item.SerialNumber !== undefined) {
        item.SNo = item.SerialNumber;
        delete item.SerialNumber;
    }
});

Try something like this

object.forEach(function(obj){
  if(obj.hasOwnProperty("SerialNumber")){
    obj["SNo"] = obj["SerialNumber"];
    delete obj["SerialNumber"];
  }
});

Check for the key after getting the objects from array.

object.forEach(function (key) {
    if ('SerialNumber' in key) {
        key.SNo = key.SerialNumber;
        delete key.SerialNumber;
    }
});

It will work if the object has no element.

When you want to change the key of the object in a array then you better prefer mapping the array elements to itself.

Here is an example.

var object = [{
        "SerialNumber": 001,
        "name": "user1"
        }, {
        "SerialNumber": 002,
        "name": "user2"
       }];
    object = object.map(function(value) {
       var tempObj = value;
       if (tempObj.SerialNumber) {
         tempObj.SNo = tempObj.SerialNumber;
         delete tempObj.SerialNumber;
       }
       return tempObj;
    });

    console.log(object);

You have to move the if condition into the forEach callback. Otherwise it will only look for the SerialNumber of the first element and crash if it doesn't exists.

var array = [{
    "SerialNumber": 001,
    "name": "user1"
}, {
    "SerialNumber": 002,
    "name": "user2"
}];
array.forEach(function (element) {
    if(element.SerialNumber) {
        element.SNo = element.SerialNumber;
        delete element.SerialNumber;
    }
});
console.log(array);