undefined[] is missing the following properties from type

Question

I have this error when I try to assign an empty value to an array whose type was already declared. Here is the code that causes the error,

export interface EmiCalculator {
    emi: number;
    months: number;
    position: number;
    principal: number;
    roi: number;
}

Below is the line that produces the error,

emiResults: EmiCalculator = [];

How can I assign an empty array to a property whose type was already declared.

score 3 · Accepted Answer · answered Aug 25 '20 at 18:39

3

EmiCalculator is an object, [] is an array. You probably want an array of EmiCalculator which can be written as EmiCalculator[] or Array<EmiCalculator>

export interface EmiCalculator {
    emi: number;
    months: number;
    position: number;
    principal: number;
    roi: number;
}
const emiResults: EmiCalculator[] = [];

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answered Aug 25 '20 at 18:39

Titian Cernicova-Dragomir

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what is the difference between Array = []; & emiResults: EmiCalculator[] – anonymous Aug 25 '20 at 18:44
@anonymous none, different way to write the same type – Titian Cernicova-Dragomir Aug 25 '20 at 18:48
Thanks for answering. – anonymous Aug 25 '20 at 18:52

score 1 · Answer 2 · answered Aug 25 '20 at 18:39

1

You are assign an array to an object.

An Interface essentially define the structure for an object, so you can't assign an array to an object.

What you might be looking for is

emiResults: Array<EmiCalculator> = [];

answered Aug 25 '20 at 18:39

Nicolas

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what is the difference between Array = []; & emiResults: EmiCalculator[] – anonymous Aug 25 '20 at 18:44
[There is a few minor differences](https://stackoverflow.com/questions/36842158/arraytype-vs-type-in-typescript), but in your case, it does not matter – Nicolas Aug 25 '20 at 18:48
Thanks for answering. Upvoted your answer. Could not accept more than two answers. – anonymous Aug 25 '20 at 18:53
It's fine, Titian was faster than me and their answer is pretty good. – Nicolas Aug 25 '20 at 18:54

Arif Rabbani · Answer 3 · 2020-08-25T18:58:43.753

-1

When you write

emiResults: EmiCalculator = [];

you are assigning an empty array to a variable emiResults whose type is defined to be EmiCalculator.

Interface defines the structure of an object. So the type of emiResults is object. But you are assigning an array.

You may want to do either of the following.

let emiResults: EmiCalculator[] = [];

or you can use the Typescript generic syntax,

let emiResults: Array<EmiCalculator> = [];

edited Aug 25 '20 at 18:58

answered Aug 25 '20 at 18:52

Arif Rabbani

9
1

How is your answer different than others? They are exactly same as others posted here. – anonymous Aug 25 '20 at 19:48
Yes, the answer is the same. I just wanted to explain a bit. – Arif Rabbani Aug 26 '20 at 02:35

undefined[] is missing the following properties from type

3 Answers3