// The 'as' keyword asserts that a variable has a type.                     =>

// TypeScript throws an error if these types have no overlap.

​

// The following example will work with jQuery.

​

let inputElt = $("#text_input");

// type of inputElt is JQuery<HTMLElement>

​

let inputValue = inputElt.val();

// type of inputValue is string | string[] | null | undefined

​

// If we are sure that the input element is a valid element and is only

// present once, the value must be of type string.

​

// Thus we can assert it is a string, as so:

let inputValueAsString = inputValue as string;

​

// If you want to learn more, click the link in the source.

interface Person {

  name: string;

  age: number;

}

​

const data: any = { name: 'John', age: 25, city: 'New York' };

​

// Using type assertion to tell TypeScript that data is a Person

const personData = data as Person;

​

// Now you can access properties as if data were a Person

console.log(personData.name); // 'John'

console.log(personData.age);  // 25