interface Cat {
meow(words: string): string;
}
interface Cat {
meow(num: number): number;
}
const cat: Cat = {
meow(wordsOrNum): string | number {
return wordsOrNum;
}
}
In the example code above, interfaces demonstrate how declarations can be merged.
However, encountering an error when attempting to implement a function within an object raises the question of its feasibility.
To ensure TypeScript recognizes the input value as equivalent to the return value, you can follow these steps:
interface Cat {
makeSound(noise: string): string;
}
interface Cat {
makeSound(num: number): number;
}
const cat: Cat = {
makeSound<Input extends string | number>(noiseOrNum: Input): Input {
return noiseOrNum;
}
}
Based on the type definition
makeSound(noiseOrNum): string | numbernoiseOrNum could be a number and the return type could be a string, or vice versa.
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