Test for array of string type in TypeScript

Question

How can I test if a variable is an array of string in TypeScript? Something like this:

function f(): string {
    var a: string[] = [\"A\", \"B\", \"C\"];

         


        

Answer 1

Here is the most concise solution so far:

function isArrayOfStrings(value: any): boolean {
   return Array.isArray(value) && value.every(item => typeof item === "string");
}

Note that value.every will return true for an empty array. If you need to return false for an empty array, you should add value.length to the condition clause:

function isNonEmptyArrayOfStrings(value: any): boolean {
    return Array.isArray(value) && value.length && value.every(item => typeof item === "string");
}

There is no any run-time type information in TypeScript (and there won't be, see TypeScript Design Goals > Non goals, 5), so there is no way to get the type of an empty array. For a non-empty array all you can do is to check the type of its items, one by one.