Error in AngularX TS: Trying to invoke a type that does not have a callable signature

Encountering an issue while working on a component, specifically during ng serve/build process. Please note that this error is different from any console errors, despite what some may think. The expected outcome is for the code to successfully build and run.

TS error TS2349: Cannot invoke an expression whose type lacks a call signature

The error occurs within the foreach function in ngOnInit()

  import { Component, OnInit, Input } from '@angular/core';
    import { ChartInput, MultiChartInput, ChartColorScheme } from "@shared/models/chart-input";

    @Component({
        selector: 'chart-legend',
        templateUrl: './chart-legend.component.html',
        styleUrls: ['./chart-legend.component.css']
    })
    export class ChartLegendComponent implements OnInit {

        @Input()
        public chartInput: ChartInput[] | MultiChartInput[];
        @Input()
        public legendColors: ChartColorScheme;

        public legends: Map<string, string> = new Map<string, string>();
        constructor() { }

        ngOnInit() {
            this.chartInput.forEach(
                (item, index) => {
                    this.legends.set(item.name, this.legendColors.domain[index]);
                });
            }
        }

export class ChartInput {
    name: string;
    value: number;

}
export class MultiChartInput {
    name: string;
    series: ChartInput[];
}
export class ChartColorScheme {
    domain: string[];
}

Any assistance in resolving this issue is greatly appreciated. If anyone believes it may be related to this question, please clarify why you think so as I am uncertain.

Answer №1

When utilizing union types, it is common to encounter a specific issue as described in Microsoft/TypeScript - Issue #7294. The issue comment explains that:

The absence of an intersectional call signature when retrieving members of a union type is intentional. Only identical call signatures will appear on the combined type.

In this scenario, the lack of compatible attributes between ChartInput and MultiChartInput causes an error. For example, ChartInput has value: number, while MultiChartInput has series: ChartInput[]. Removing these attributes temporarily can help verify the issue (experiment demo).

To resolve the error without compromising type safety, adjust the type of chartInput to (ChartInput | MultiChartInput)[]:

class ChartLegendComponent implements OnInit {
    public chartInput: (ChartInput | MultiChartInput)[];
    ...
}

Fix option 1 demo

Alternatively, cast this.chartInput:

(this.chartInput as (ChartInput | MultiChartInput)[])
  .forEach(
      (item, index) => {
          this.legends.set(item.name, this.legendColors.domain[index]);
      });
  }

Fix option 2 demo

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