https://i.stack.imgur.com/htnkb.png
type Test = number[][]; // The Test type will be inferred as 'number' based on the image above.
Can you explain why number[] is considered an index signature type with a signature of 'number'?
https://i.stack.imgur.com/htnkb.png
type Test = number[][]; // The Test type will be inferred as 'number' based on the image above.
Can you explain why number[] is considered an index signature type with a signature of 'number'?
This showcases a method for obtaining the union of different types of values.
Here's another way to look at it: if you have an array of numbers represented as number[], when we use [number], we are essentially asking for a combination of types of values that fall under numeric keys. Since the array consists of numbers, the resulting type will be number.
type TestObject = {
test1: string;
test2: number;
};
// The union of all keys results in string | number
type TestValueUnion = TestObject[keyof TestObject];
// 'test1' | 'test2'
type TestKeyUnion = keyof TestObject;
array of numbers is indicated by number[]
If you need to determine the type of array, simply add [randomInput]
thus number[][number] indicates the type of number[]
number[][xxx] can also be represented as number - give it a try!
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