After successful jquery Ajax request, eval (data) error syntaxerror:missing; Before statement

In a single request

$.ajax ({
Cache:true,
Type: "POST",
URL: "Getdatalist.action",
Async:false,
Error:function (Request) {
Alert ("Connection error");
},
Success:function (data) {
var jsondata = eval (data);
$ ("#weather"). Val (Jsondata.weatherinfo);
}
});

Error: syntaxerror:missing; Before statement

Very angry obviously no less, but the hint of error, search on the internet a lot of answers are the special symbols plus escape character method but not for my this

It was later discovered that the datatype needed to be specified: ' JSON ' can be perfectly solved

$.ajax ({
Cache:true,
Type: "POST",
URL: "Getdatalist.action",
Async:false,
DataType: ' JSON ',
Error:function (Request) {
Alert ("Connection error");
},
Success:function (data) {
Jsondata = eval (data);
$ ("#weather"). Val (Jsondata.weatherinfo);
}
});

Additional: In JS to get the JSON result passed in the background, generally using var res=eval (${data}) instead of using Var res= ' ${data} '

Ajax request background does not error but always executes the error function method

Cause this

1 You may have used asynchronous commit (Async=true)

2 You specified the datatype in the AJAX request, but the parameters you sent back were not passed in the type you specified.