In this article, we are going to learn the different ways of asserting the type of an HTMLElement in TypeScript. The type assertion is used to type the simple variables to JavaScript objects by defining the HTML element name.
There are many ways of performing this task as listed below:
Table of Content
Typing using the colon syntax
This is the general way of typing the variables in TypeScript that can also be used to assert the HTMLElement as well in TypeScript.
Syntax:
const var_name: type = value;Example: The below example will show you how the colons can be used to assert HTMLElement in TypeScript.
const appDiv: HTMLElement = document.getElementById('app');
appDiv.innerHTML = `<h1>
${typeof appDiv}
</h1>`; |
<!DOCTYPE html><html>
<head>
<title>Page Title</title>
</head>
<body>
<h2>Welcome To GFG</h2>
<div id="app"></div>
</body>
</html>
|
Output:
ObjectUsing <> to assert typecast
In this approach, we will assert the type by specifying it inside the angular brackets (<>) just before the document selection of the element.
Syntax:
const var_name = <HTMLType> document.getElementById(ID');Example: The below example will explain how you can assert HTMLElement using the angular brackets syntax.
const appDiv = <HTMLDivElement>document.
getElementById('app');
appDiv.innerHTML = `<h1>
${typeof appDiv}
</h1>`; |
<!DOCTYPE html><html>
<head>
<title>Page Title</title>
</head>
<body>
<h2>Welcome To GFG</h2>
<div id="app"></div>
</body>
</html>
|
Output:
ObjectUsing item() method with asserting type
In this approach, we will select the typecasting element using the tagname and the item() method and then type it using as typingProperty.
Syntax:
const var_name = document.getElementsByTagName('tag_name').item(0) as assertionTypeExample: The below example will show the use of the item() method to assert type.
const appDiv = document.getElementsByTagName('div').
item(0) as HTMLDivElement;
appDiv.innerHTML = `<h1>
${typeof appDiv}
</h1>`; |
<!DOCTYPE html><html>
<head>
<title>Page Title</title>
</head>
<body>
<h2>Welcome To GFG</h2>
<div id="app"></div>
</body>
</html>
|
Output:
ObjectUsing the any type with asserting type
This approach will use the <any> type after the specified asserting type and define booth of them before accessing the element from DOM.
Syntax:
const var_name = (<assertingType> <any> document.getElementsByTagName('tag_name'))[0];Example: The below example will show how to assert type with the help of the any type.
const appDiv = (<HTMLDivElement><any>document.
getElementsByTagName('div'))[0];
appDiv.innerHTML = `<h1>
${typeof appDiv}
</h1>`; |
<!DOCTYPE html><html>
<head>
<title>Page Title</title>
</head>
<body>
<h2>Welcome To GFG</h2>
<div id="app"></div>
</body>
</html>
|
Output:
Object