Issues with expected identifiers and type mismatch errors encountered when defining a TypeScript class

As someone who is still relatively new to coding, I am facing a challenge while trying to create a TypeScript class within an Angular project that is based on a complex JSON file. The issue arises from the way the properties were defined in the JSON using string literals. I am uncertain if this is the root cause of the errors I am encountering, and I am seeking guidance on the correct way to declare these properties in TypeScript. Interestingly, when I declare the properties explicitly, everything appears to be in order...

// Initial property declarations seem to be correct
export class State {
    'FIPS Code': number;
    'Postal': string;
    'Area Name': string;
    'Less than a high school diploma, 1970': number;
... 
}

However, when attempting to create a constructor function, I am faced with various errors...

// Errors occur with all parameter identifiers indicating 'identifier expected'
constructor('FIPS Code': number, 'Postal': string,
        'Area Name': string,
        'Less than a high school diploma, 1970': number,
        'High school diploma only, 1970': number,
...) {

    // Type '"FIPS Code"' is not assignable to type 'number'
    this['FIPS Code'] = 'FIPS Code';

    // The next two assignments are successful, presumably because they are strings
    this['Postal'] = 'Postal';
    this['Area Name'] = 'Area Name';

    // The remaining assignments result in errors indicating not assignable to type 'number'
    this['Less than a high school diploma, 1970'] = 'Less than a high school diploma, 1970';
...
}

Answer №1

Avoid mixing variables, keys, and strings in your code.

When accessing data within an object, you can use a string as a key. However, variables (such as arguments of a constructor) should adhere to naming conventions.

// all parameter identifiers say 'identifier expected'
constructor(FIPSCode: number, Postal: string,
        AreaName: string,
        Lessthanahighschooldiploma1970: number,
        Highschooldiplomaonly1970: number,
...) {

    // Type '"FIPS Code"' is not assignable to type 'number'
    this['FIPS Code'] = FIPSCode;

    // the next two are ok, I assume because they're strings
    this['Postal'] = Postal;
    this['Area Name'] = AreaName;

    // everything else remaining says not assignable to type 'number'
    this['Less than a high school diploma, 1970'] = Lessthanahighschooldiploma1970;
...
}

For more information on declaring variables, refer to: https://www.typescriptlang.org/docs/handbook/variable-declarations.html

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