[jQuery] How can I use VAR str into json object

[jQuery] How can I use VAR str into json object


var str = "hello";
var json = {
str: "123"
}
I know this is not jquery question , but I don't know where I should
go
The question is how can I use VAR str into json object, I don't want
{"str": 123}, actually i want {"hello": 123}
How can solve this problem? In fact this question troubling me a long
time
Thank you for the answer, any input will help