Author: John Au-Yeung

Sometimes, we want to set an object to the Date type with TypeScript.

In this article, we’ll look at how to set an object to the Date type with Typescript.

How to set an object to the Date type with TypeScript?

To set an object to the Date type with TypeScript, we can use the Date type.

For instance, we write

const d: Date = new Date();

to set the variable d to have type Date and assign it to a Date instance.

Conclusion

To set an object to the Date type with TypeScript, we can use the Date type.

Sometimes, we want to fix "The property ‘value’ does not exist on value of type ‘HTMLElement’" error with TypeScript.

In this article, we’ll look at how to fix "The property ‘value’ does not exist on value of type ‘HTMLElement’" error with TypeScript.

How to fix "The property ‘value’ does not exist on value of type ‘HTMLElement’" error with TypeScript?

To fix "The property ‘value’ does not exist on value of type ‘HTMLElement’" error with TypeScript, we should cast our HTML object to a HTMLInputElement.

For instance, we write

const inputValue = (<HTMLInputElement>document.getElementById(elementId)).value;

to cast the object returned by document.getElementById(elementId) to an HTMLElementInput.

Likewise, we can do the same with as by writing

const inputValue = (document.getElementById(elementId) as HTMLInputElement)
  .value;

Conclusion

To fix "The property ‘value’ does not exist on value of type ‘HTMLElement’" error with TypeScript, we should cast our HTML object to a HTMLInputElement.

Sometimes, we want to add a class type check in TypeScript.

In this article, we’ll look at how to add a class type check in TypeScript.

How to add a class type check in TypeScript?

To add a class type check in TypeScript, we can create a function to do the check.

For instance, we write

const isFish = (pet: Fish | Bird): pet is Fish => {
  return (<Fish>pet).swim !== undefined;
};

if (isFish(pet)) {
  pet.swim();
} else {
  pet.fly();
}

to create the isFish function that returns the pet is Fish type.

And we check if pet is a Fish by checking if the swim property isn’t undefined.

Then we call isFish with pet to check if pet is a Fish.

And then we call swim if it is a Fish.

Conclusion

To add a class type check in TypeScript, we can create a function to do the check.

Sometimes, we want to fix the "error TS2533: Object is possibly ‘null’ or ‘undefined’" error with TypeScript.

In this article, we’ll look at how to fix the "error TS2533: Object is possibly ‘null’ or ‘undefined’" error with TypeScript.

How to fix the "error TS2533: Object is possibly ‘null’ or ‘undefined’" error with TypeScript?

To fix the "error TS2533: Object is possibly ‘null’ or ‘undefined’" error with TypeScript, we can use the optional chaining operator.

For instance, we write

refToElement?.current?.focus();

to use the optional chaining ?. to get the value of the refToElement.current.focus method.

?. will return undefined if any of the properties in the chain are null or undefined instead of throwing an error.

Conclusion

To fix the "error TS2533: Object is possibly ‘null’ or ‘undefined’" error with TypeScript, we can use the optional chaining operator.

Sometimes, we want to get an object’s class name at runtime with TypeScript.

In this article, we’ll look at how to get an object’s class name at runtime with TypeScript.

How to get an object’s class name at runtime with TypeScript?

To get an object’s class name at runtime with TypeScript, we canm use the name property of the constructor or class.

For instance, we write

class MyClass {}

const x = new MyClass();

console.log(x.constructor.name);
console.log(MyClass.name);

to get the name property from a MyClass instance with x.constructor.name.

Likewise, we get the class name from the static MyClass.name property.

They should both return 'MyClass'.

Conclusion

To get an object’s class name at runtime with TypeScript, we canm use the name property of the constructor or class.