Typescript type string is not assignable to type keyof "Interface"

Question

I have the following code

export interface A {
  redApple: props[];
  yellowApple: props[];
  redYellowApple: props[];

}

export type FruitColour = "red" | "yellow | "green";
export type Fruit = "apple" | "banana | "cherry";

const x = [
  "redApple",
  "yellowApple",
  "redYellowApple",
  "greenCherry"
]

export const changeFruit = (
  fruit: Fruit,
  colour: Colour
): keyof A => {
  return x
    .filter((string) => string.match(colour + fruit))
    .splice(0, 1)
    .toString();
};

I keep getting Type 'string' is not assignable to type 'keyof IndexViewDataItem'. I can use myFunction(someField: keyof A | string) but then I lose type guarding.

Any help or guidance would be greatly appreciated.

Also note that your array entries seem to be in colour-fruit order, but you're comparing using fruit + colour. Also, array is an odd name for a parameter that will be a string, not an array. And the match method probably isn't what you're looking for there. — T.J. Crowder
– T.J. Crowder, Commented May 23, 2021 at 10:47
Hi sorry about that. I have edited the question. Fruit and Colour are both types. Array was odd it should be string. The goal of the funcstion is to return the closest match to the inputed colour and fruit from array x, so match(green, cherry) would return green cherry. I then feed that response as a field parameter to the myFunction(someField: keyof A) — PengProgrammer
– PengProgrammer, Commented May 23, 2021 at 11:37
keyof A is "colour" | "otherProperties". Your function returns string, which you can't assign to the type "colour" | "otherProperties". Also, none of the values in the array match either property name. — T.J. Crowder
– T.J. Crowder, Commented May 23, 2021 at 11:42
Wouldnt the match return the closest string? if I run that function with inputs "Green" and "Cherry" it returns greenCherry from x and yes I apologies you were correct, interface A contains the types for the strings in the array. I should have taken more time in structing the question to see what I left out. — PengProgrammer
– PengProgrammer, Commented May 23, 2021 at 11:50

PengProgrammer · Accepted Answer · 2021-05-23 12:57:30Z

1

Managed to get a work around for this by

export const changeFruit = (
  fruit: Fruit,
  colour: Colour
): keyof A => {
  const y = x
    .filter((string) => string.match(colour + fruit))
    .splice(0, 1)
    .toString();
    return y as keyof A;
};

Not sure if this still enforces type guarding but I imagine so. If not I would still appreciate a better approach.

answered May 23, 2021 at 12:57

PengProgrammer

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