Unable to perform type casting in Typescript

I recently dived into the world of TypeScript by picking up a book titled Typescript Revealed (Published in February 2013). Chapter 2 caught my attention with a section on "Casts" featuring an intriguing example:

var a : int = <int>SomeNumberAsAString;

Excited to try it out, I attempted the following implementation:

var SomeNumberAsAString = "1000";
var a: int = <int>SomeNumberAsAString;

However, much to my dismay, the compiler threw an error:

hello.ts(2,8): error TS2304: Cannot find name 'int'.
hello.ts(2,15): error TS2304: Cannot find name 'int'.

This left me contemplating how to execute this cast correctly, or if there have been updates to the TypeScript specifications.

castingtypescript

Answer №1

(Published in February 2013)

That publication is considered dated now. It's referred to as number at present.

var SomeNumberAsAString = "1000";
var a: number = <number><any>SomeNumberAsAString;

It should be noted that performing this type assertion could be risky and not recommended in a production environment. However, it serves the purpose here :)

Further Reading

A more recent chapter on type assertions can be found at: https://basarat.gitbooks.io/typescript/content/docs/types/type-assertion.html

Answer №2

After reading @basarat's response, I felt compelled to share my own thoughts as I strongly believe there is still more to be explained.

It is important to note that <number><any> casting does not actually generate a number in JavaScript. While it may allow your code to pass static typing checks during compilation, the value will not truly be a number. Consider the following example:

let str = "1000";
let a: number = <number><any>str;
let b: number = parseInt(str);

console.log(typeof a); // string
console.log(typeof b); // number

In most scenarios, using the b approach with parseInt or parseFloat is preferred over the a method. The <T><any> casting may seem clever, but it is essential to fully understand its purpose before implementing it.

In reality, you likely do not want to use this technique at all.)

Answer №3

If you want to do it the best way, try this method.

let numStr = '5000';
let b: integer = numStr as any;

Answer №4

This option is my favorite

const StringNumber = '1000';
let b = +StringNumber;
console.log(b);

Answer №5

let value: number = <number> +SomeStringAsNumber;

+SomeStringAsNumber converts the numeric string into a number.

The usage of <number> before +SomeStringAsNumber instructs the TypeScript compiler to cast the data type to number.

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