[GitHub] [echarts] ChepteaCatalin commented on issue #19064: [Bug] tooltip.formatter option is not typed correctly

["ChepteaCatalin (via GitHub)" <gi...@apache.org>]

ChepteaCatalin commented on issue #19064:
URL: https://github.com/apache/echarts/issues/19064#issuecomment-1718004681

   @yay I suggest you use the following workaround, which appears less awkward:
   
   ```typescript
           tooltip: {
               formatter: (params: echarts.DefaultLabelFormatterCallbackParams) => {
                   return `${params.name}, ${params.seriesName}`;
               }
           } as echarts.TooltipComponentOption
   ```
   
   `params` is expected to be of type `TooltipComponentFormatterCallbackParams` which is an alias for 
   
   ```typescript
   type TopLevelFormatterParams = CallbackDataParams | CallbackDataParams[];
   ```
   
   TypeScript will try to infer the most general type from the union that encompasses both possibilities even if you want to infer only `CallbackDataParams` type. In your case, `CallbackDataParams[]` is inferred because it's more general than just `CallbackDataParams`. So, you have to set explicitly that you want `CallbackDataParams`, which is exported as `DefaultLabelFormatterCallbackParams`.
   
   As mentioned in the [documentation](https://echarts.apache.org/en/option.html#tooltip.formatter), `params` can take the form of either an object or an array so I don't think that we should change anything in the library. @plainheart, what are your thoughts on this?
   
   
   


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