Creating a Request Params for batchWriteItem(params,function(){}) in javaScript - node.js

Question

I have been trying to create params for batchWriteItem(), when I create them like this it perfactly works.
var params = {
RequestItems: {
'tableNameXYZ' : [ //hardcoded
{
PutRequest: {
"Item" : {
"indexNumber":{
"N": xyz
},...
}
},
PutRequest: {
"Item" : {
"indexNumber":{
"N": xyz1
},...
}
}
}
]
};
But I am unable to work on it when I have table name in a variable:
var tableName = 'tableNameXYZ';
var params = {
RequestItems: {
tableName : [
{
PutRequest: {
"Item" : {
"indexNumber":{
"N": xyz
},...
}
},
PutRequest: {
"Item" : {
"indexNumber":{
"N": xyz1
},...
}
}
}
]
};
Obviously this wouldn't have worked since I played rough with JSON object here.
Then I tried this:
var params = {};
params.RequestItems[tableName] = [
{
PutRequest: {
"Item" : {
"indexNumber":{
"N": xyz
},...
}
},
PutRequest: {
"Item" : {
"indexNumber":{
"N": xyz1
},...
}
}
}
];
Now its throwing me an error like:
TypeError: Cannot set property 'tableNameXYZ' of undefined
at exports.handler (/var/task/index.js:181:32)
Can someone Pointout my mistake?
Thanks.

Answer 1

You've got this error because:
var params = {};
Creates an empty object (called params) with no properties, but:
params.RequestItems[tableName] = [ // ...rest of code
Tries to assign params.RequestItems.the-value-of-tableName.
But params has no property called RequestItems and so, params.RequestItems is undefined. And it is a TypeError to try and set the value of a property (in this case the-value-of-tableName) on undefined.
To fix this, use:
var params = {};
params.RequestItems = {}; // assign RequestItems an empty object.
params.RequestItems[tableName] = [ // ...rest of code.