Encountering issues with TypeScript class

I am facing an issue with transpiling the following TypeScript class:

class DataService {
    styles: Object[];
    selectedStyle: Object;
    selectedChildStyle: Object;
    
    constructor() {
        this.styles = [{
            "name": "Parent",
            "child": {}
        }];
        
        this.selectedStyle = this.styles[0];
        
        // THE BELOW LINES CAUSE AN ERROR
        if (this.selectedStyle.child && this.selectedStyle.child.length)
            this.selectedChildStyle = this.selectedStyle.child[0];
        else
            this.selectedChildStyle = null;
    }
}

Whenever I try to run npm start, the application fails to start and throws a strange error related to ELIFECYCLE. This issue seems to occur when the last four lines are uncommented.

typescript

Answer №1

The reason for the issue is because you are utilizing Object as the type for this.selectedStyle, and Object does not contain a field named child.

If you wish for the compiler to understand the types, you should define them like this:

interface Style {
    name: string;
    child: Style[];
}

class DataService {
    styles: Style[];
    selectedStyle: Style;
    selectedChildStyle: Style;

    constructor() {
        this.styles = [{
            "name": "Parent",
            "child": [<Style> {}]
        }];

        this.selectedStyle = this.styles[0];

        // THE FOLLOWING LINES CAUSE AN ISSUE
        if (this.selectedStyle.child && this.selectedStyle.child.length)
            this.selectedChildStyle = this.selectedStyle.child[0];
        else
            this.selectedChildStyle = null;
    }
}

Answer №2

Declare selectedStyle to be of type any;

selectedStyle: any; // Updated declaration

class DataService {
    styles: Object[];
    selectedStyle: any; // Updated declaration
    selectedChildStyle: Object;

    constructor() {
        this.styles = [{
            "name": "Parent",
            "child": {}
        }];

        this.selectedStyle = this.styles[0];

        if (this.selectedStyle.child && this.selectedStyle.child.length)
            this.selectedChildStyle = this.selectedStyle.child[0];
        else
            this.selectedChildStyle = null;
    }
}

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