We can also define an interface for array types. We can specify the data type for the index array and the data type to the array item, as shown:

interface CutomerNameArray { 
  [index: number]: string; 
}  
let customerNameList: CutomerNameArray; 
customerNameList = ["Rajesh", "Gunasundaram"]; 

TypeScript supports two types of index, namely number, and string. This array type interface also enforces that the return type of the array should match the declaration.