ERROR TypeError: "item.toJSON is not a function

I have a parent object with a collection of children object:

public class EnduserCartModel
{
     ...
     public ICollection<ProductListModel> products {get;set;}
}

In controller :

[HttpPost("")]
... ([FromBody]EnduserModel enduserModel)
{
     ...
}

At the moment of sending the object from Angular to the Server I got this error: ERROR TypeError: "item.toJSON is not a function. This error appears on this line: data["products"].push(item.toJSON());

The code is generated by NSwag Studio: 13.6.0.0 . So here the bug.

[andmattia]

Hi have the same error (V. 13.5.0) but I found the problem in my case is related to a cast.

args.columns = <EntityDto[]>columns; // Fail on toJSON

I see in debug that my object is not create from EntityDto and toJSON in not available I change with this

 let colTyped : EntityDto[] = [];
        if(columns != undefined){
            for(var idx=0; idx < columns.length;idx++){
                var addCol = new EntityDto();
                addCol.technicalName = columns[idx].technicalName;
                colTyped.push(addCol);
            }
        }

And toJSON is valid function

[Radwa-Moustafa]

I came across this issue multiple times and the solution was to make sure that your “item” is an instance of “ProductListModel” in front-end while you’re appending this object to your array before sending it to the back end so when it calls .toJSON() in service-proxies.ts it will find .toJSON() in your object and it will not throw that exception anymore.