电子图表工具提示 Typescript

Question

I'm using eChart v5.0.2 and working to customize the tooltip using Typescript, but can't seem to resolve this error regarding the formatter.

So on the function keyword, the error message states: Type '(params: Format | Format[]) => string | Formatter' is not assignable to type 'string | Formatter | undefined'.

And on the params.value, the error is: Type '(params: Format | Format[]) => string | Formatter' is not assignable to type 'string | Formatter | undefined'.

I would really appreciate any help with this thanks!

This is the code that I have:

            let option: echarts.EChartOption = {
                xAxis: {},
                yAxis: {},
                series: [{
                    symbolSize: 20,
                    data: chartData,
                    type: 'scatter'
                }],
                tooltip: {
                    showDelay: 0,
                    formatter: function (params): (string | echarts.EChartOption.Tooltip.Formatter) {
                       
                        if (params) {
                            let xValue = params.value[0];
                            let yValue = params.value[1];
                            let dttmValue = params.value[2];

                            return xValue + yValue + dttmValue;
                        }

                        return '';
                    },
                },
            };

            option && chart.setOption(option);```

Answer 1

It looks like the formatter value is meant to actually BE a echarts.EChartOption.Tooltip.Formatter function but in your declaration of your formatter function you are effectively saying your formatter property is a function that RETURNS a formatter function.

The bit that says : (string | echarts.EChartOption.Tooltip.Formatter) is the part where you explicitly declare the return type of your function. Not what you intend I think.

It looks like the type your formatter value is MEANT to conform to is described at https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/echarts/options/tooltip.d.ts#L390 which is to say it should be a function that returns a string so probably : string to define the return value would be enough - or just return only strings from the function and Typescript will infer that it's the right kind of function to be a formatter.