What is the method to retrieve the data type of an array in TypeScript?

Question

What is the method to retrieve the data type of an array in TypeScript?

I am currently working on a TypeScript function (still getting acquainted with TS) that accepts a parameter which could be either a number, a string, an array of numbers, or an array of strings.

It is crucial for me to distinguish between these 4 types within my code.

When I use typeof on an array, it always returns 'object'. How can I differentiate between an array of strings and an array of numbers in my code?

I understand that I could utilize for loops or array methods to determine the type of each element in the array, but I am wondering if there is a more elegant solution.

function numToLet(input: number | number[] | string | string[]) {

if (typeof input === 'number') {
    console.log(`The input ${input} is a number.`)
}

if (typeof input === 'string') {
    console.log(`The input ${input} is a string.`)
}

if (typeof input === 'object') {
    console.log(`The input ${input} is an object. Not sure about its specific type though ¯\_(ツ)_/¯`)
}

}

arrays typescript

Answer 1

Answer №1

Have you explored the Array method known as Array.isArray()? It can be found at this link. I tend to use it quite frequently, perhaps even excessively.

In a previous project where strict mode was not enabled, I found Array.isArray() to be incredibly useful in handling both null values and unexpected inputs.

const myActualArray = ['apple', 'banana'];
const myUnArray = "apples and bananas";
let oops;

console.log(Array.isArray(myActualArray)); // true
console.log(Array.isArray(myUnArray)); // false
console.log(Array.isArray(oops)); // false
console.log(Array.isArray(null)); // false

On another note, have you delved into TypeScript generics? I'm just beginning to explore them myself, so I cannot confidently say if they offer a suitable TypeScript solution for your needs - keep in mind that Array.isArray() is specifically a JavaScript solution. You can learn more about TypeScript generics here.

An additional point to consider after reading your comment: It appears that you are relying heavily on your code to handle one of four input types. By combining the utilization of typeof with Array.isArray, you can streamline this process.

function numToLet(input: number | number[] | string | string[]) {

  if (typeof input === 'number') {
      console.log(`Input ${input} is a number.`)
  }

  if (typeof input === 'string') {
      console.log(`Input ${input} is a string.`)
  }

  if (Array.isArray(input)) {
      // If you're confident that your array consists solely of either all numbers or all strings, simply check the type of the first element.
      if (typeof input[0] === 'number') {
        console.log(`Input ${input} is a number.`)
      }

      if (typeof input[0] === 'string') {
        console.log(`Input ${input} is a string.`)
      }
  }
}

Answer 2

Have you explored the Array method known as Array.isArray()? It can be found at this link. I tend to use it quite frequently, perhaps even excessively.

In a previous project where strict mode was not enabled, I found Array.isArray() to be incredibly useful in handling both null values and unexpected inputs.

const myActualArray = ['apple', 'banana'];
const myUnArray = "apples and bananas";
let oops;

console.log(Array.isArray(myActualArray)); // true
console.log(Array.isArray(myUnArray)); // false
console.log(Array.isArray(oops)); // false
console.log(Array.isArray(null)); // false

On another note, have you delved into TypeScript generics? I'm just beginning to explore them myself, so I cannot confidently say if they offer a suitable TypeScript solution for your needs - keep in mind that Array.isArray() is specifically a JavaScript solution. You can learn more about TypeScript generics here.

An additional point to consider after reading your comment: It appears that you are relying heavily on your code to handle one of four input types. By combining the utilization of typeof with Array.isArray, you can streamline this process.

function numToLet(input: number | number[] | string | string[]) {

  if (typeof input === 'number') {
      console.log(`Input ${input} is a number.`)
  }

  if (typeof input === 'string') {
      console.log(`Input ${input} is a string.`)
  }

  if (Array.isArray(input)) {
      // If you're confident that your array consists solely of either all numbers or all strings, simply check the type of the first element.
      if (typeof input[0] === 'number') {
        console.log(`Input ${input} is a number.`)
      }

      if (typeof input[0] === 'string') {
        console.log(`Input ${input} is a string.`)
      }
  }
}

What is the method to retrieve the data type of an array in TypeScript?

Answer №1

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