angular - Why TypeScript gives the error message Property 'value' does not exist on type 'unknown'?

Question

I have the below function:

myChart.on('click', { targetType: 'axisLabel' }, params => {
      var uri = window.location.hash.replace("#", "");
      this.router.navigate([uri + '/trips', params.value]);
    })

This function returns the error message:

Property 'value' does not exist on type 'unknown'.

The given params contains value. But this error keeps popping up. How do I resolve it?

Answer 1

You need to add a type annotation to params. Otherwise the compiler cannot infer its type, and thus cannot know if it actually has the value property.

E.g.

interface Params {
    value: string
}

myChart.on('click', { targetType: 'axisLabel' }, (params: Params): void => {
    var uri = window.location.hash.replace("#", "");
    this.router.navigate([uri + '/trips', params.value]);
});