TypeScript Error: Property '0' is missing in type

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I have my interface like this

export interface Details {
  Name: [{
    First: string;
    Last: string;
  }];
}   

I have an observable config variable:

Configuration: KnockoutObservable<Details> = ko.observable<Details>();

and I would like to assign it a value in the constructor as follows:

config = {
  Name: [{
    First: "ABC",
    Last: "DEF"
  },
  {
    First: "LMN",
    Last: "XYZ"
  }]
};

this.Configuration(config);

and I am getting an error:

Types of property 'Name' is incompatible and property '0' is missing in type.
Type '{ First:string; Last:string; }[]' is not assignable to 
type '[{ First: string; Last:string; }]'

I don't have control on changing the interface as it is being used elsewhere. What is the correct way to initialize this config variable ?

Thanks in advance.

I came across the same issue and got around it by changing the interface to:

    interface Details {
        Name: {
            First: string;
            Last: string;
        }[];
    }

I know you may not want the interface changed but hope this helps for anyone that is in this situation.

TypeScript 2.2 � TypeScript, The reason for your error in your initial code is because you are telling the TypeScript compiler that data is of type Object or any derived class from that - as the type Object has no properties a or b this results in an error. lineInfo.PublishedLineName is declared as a string, and String.prototype.includes() is a function according to MDN, so why does the TypeScript compiler complain about the missing property/method? lineInfo.PublishedLineName

This error can come from incorrectly typing an array (like I just did):

myArray:[]; //Incorrect, results in error message of `Property '0' is missing in type`

myArray: Array<string>; //Correct

myArray: string[]; //Also correct

The reason is that braces denote a tuple in Typescript, not an array.

The Docs

TypeScript error when accessing property of object literal, When compiled/transpiled through TypeScript it generates error TS2339: Property 'myclassvar' does not exist on type 'MyClass'. If the above� When compiled/transpiled through TypeScript it generates error TS2339: Property 'myclassvar' does not exist on type 'MyClass'. If the above code snippet is valid ES6 then TypeScript should not generate the error. The generated javascript it valid. It's just that the error scares the developers trying to use ES6 without typings.

In this type definition:

interface Details {
  Name: [{
    First: string;
    Last: string;
  }];
}

Name is not an array at compile-time. It's a tuple with one element. Tuples in Typescript are allowed to have extra elements, but they can't have missing elements. As a 1-tuple, Name is essentially an array which must have at least one element.

However, in this value:

const config = {
  Name: [{
    First: "ABC",
    Last: "DEF"
  },
  {
    First: "LMN",
    Last: "XYZ"
  }]
};

Since there is no explicit typing, the Name property here defaults to array type. Arrays can have any number of elements, including zero - which doesn't fit in a 1-tuple. Hence your error.

Your error can be fixed by giving the compiler a hint that your literal is actually a tuple:

const config: Details = { Name: [{...}, {...}] };

If you do need to be able to take in an array of names, you'll have to do some casting, maybe something like this:

if (names.length > 0) {
  const config = {
    Name: names as Details['Name']
  };
  Configuration(config);
}

(You could remove the if check if you can determine that the tuple was simply a mistake by whoever wrote the typings.)

Tuples reference: https://www.typescriptlang.org/docs/handbook/basic-types.html

Getting error TS2339: Property does not exist on type for a valid ES6 , New error: Property 'value' does not exist on type 'never' #37565. Closed amcasey added this to the TypeScript 3.9.1 milestone on Mar 24. When it comes to TypeScript’s private property declarations, users still have to be careful not to trample over properties declared in superclasses. One more thing to think about is where you intend for your code to run. TypeScript currently can’t support this feature unless targeting ECMAScript 2015 (ES6) targets or higher.

Updating the interface to following should fix the issue :

 interface Details {
        Name: Array<{
            First: string;
            Last: string;
        }>;
    }

New error: Property 'value' does not exist on type 'never' � Issue , Error:(54, 6) TS2339:Property 'name' does not exist on type '{}'. So what is going here? We have defined an empty object first and then tried to� Previously, it was only an error for properties to override accessors, or accessors to override properties, when using useDefineForClassFields; however, TypeScript now always issues an error when declaring a property in a derived class that would override a getter or setter in the base class.

Typescript 2 Type System: How Does it Really Work? Type , toUppercase(); // ~~~~~~~~~~~ // error: Property 'toUppercase' does not exist on type 'string'. // Did you mean 'toUpperCase� The unknown Type in TypeScript May 15, 2019. TypeScript 3.0 introduced a new unknown type which is the type-safe counterpart of the any type.. The main difference between unknown and any is that unknown is much less permissive than any: we have to do some form of checking before performing most operations on values of type unknown, whereas we don't have to do any checks before performing

Announcing TypeScript 3.7, But they also may have other properties of their own, e.g. HttpError objects may have a statusCode property with a value like 404 or 403 or 500 . We can prefix the constructor parameters with the public or private keyword to automatically have TypeScript assign the parameter as a property of the class. In this example, this removes the unnecessary declaration and assignment of both firstName and lastName. TypeScript Private Methods

Custom errors, extending Error, It means only an object with properties key of number type and value of string type can be assigned to a variable kv1 . The TypeScript compiler will show an error� Compiling TypeScript. TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. It offers classes, modules, and interfaces to help you build robust components.

Comments
  • I want to kiss you! I fought this for so long without any answers. Thanks you so much!
  • Ha! I am glad this helped because I definitely found myself in the same boat some time ago.
  • Just in case it isn't obvious the solution here is to move the [] to immediately follow {} instead of being [ { } ]. This is a change in syntax with recent typescript version.
  • This should be the correct answer IMO.
  • great answer! just helped me out.
  • Can you explain why this fixes the issue please?
  • I believe, [] in typescript refers to tuple type , Array<> is a closer representation of javascript arrays. That's my understanding .