Justyn  Ortiz

Justyn Ortiz

1606722540

Type checking in JavaScript: Typeof and Instanceof Operators

Learn how to perform type checking in JavaScript using typeof and instanceof operators.

JavaScript is a loosely-typed language, so there is no restriction on the variable’s type.

For example, if you’ve created a variable with a string type, later you can assign to the same variable a number:

let message = 'Hello'; // assign a string

message = 14; // assign a number

Such dynamism gives you flexibility and simplifies variables declaration.

On the other side, you can never be sure that a variable contains a value of a certain type. For example, the following function greet(who) expects a string argument, however, you can invoke the function with any type of argument:

function greet(who) {
  return `Hello, ${who}!`
}

greet('World'); // => 'Hello, World!'
// You can use any type as argument
greet(true);    // => 'Hello, true!'
greet([1]);     // => 'Hello, 1!'

That’s why, sometimes, you need to check the variable’s type in JavaScript — using typeof operator, as well as instanceof to check instance types.

Let’s see in more detail how to use typeof and instanceof operators in JavaScript.

  • typeof operator
    • typeof null
    • typeof and not defined variables
  • instanceof operator
    • instanceof and the parent class

#javascript #web-development #testing #programming

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Type checking in JavaScript: Typeof and Instanceof Operators
Coy  Roberts

Coy Roberts

1599716220

Javascript Typeof Example | typeof Operator Tutorial

Javascript typeof is an inbuilt operator that returns the string indicating a type of the unevaluated operand. JavaScript typeof operator returns a data type of its operand in the form of the string. The operand can be any object, function or variable. You can use a JavaScript typeof operator to find the type of the JavaScript variable. The typeof operator returns the type of the variable or an expression.

Javascript Typeof Example

Let’s see the syntax of the typeof operator.

typeof operand

The operand parameter is an expression representing the object or primitive whose type is to be returned. See the following example.

// app.js

console.log(typeof 'appdividend');

#javascript #javascript typeof #typeof operator #typeof

Santosh J

1622036598

JavaScript compound assignment operators

JavaScript is unarguablly one of the most common things you’ll learn when you start programming for the web. Here’s a small post on JavaScript compound assignment operators and how we use them.

The compound assignment operators consist of a binary operator and the simple assignment operator.

The binary operators, work with two operands. For example a+b where + is the operator and the a, b are operands. Simple assignment operator is used to assign values to a variable(s).

It’s quite common to modify values stored in variables. To make this process a little quicker, we use compound assignment operators.

They are:

  • +=
  • -+
  • *=
  • /=

You can also check my video tutorial compound assignment operators.

Let’s consider an example. Suppose price = 5 and we want to add ten more to it.

var price = 5;
price = price + 10;

We added ten to price. Look at the repetitive price variable. We could easily use a compound += to reduce this. We do this instead.

price += 5;

Awesome. Isn’t it? What’s the value of price now? Practice and comment below. If you don’t know how to practice check these lessons.

Lets bring down the price by 5 again and display it.
We use console.log command to display what is stored in the variable. It is very help for debugging.
Debugging let’s you find errors or bugs in your code. More on this later.

price -= 5;
console.log(price);

Lets multiply price and show it.

price *=5;
console.log(price);

and finally we will divide it.

price /=5;
console.log(price);

If you have any doubts, comment below.

#javascript #javascript compound assignment operators #javascript binary operators #javascript simple assignment operator #doers javascript

Javascript Instanceof Operator Example | Instanceof in Javascript

Javascript instanceof is an inbuilt operator that tests whether a prototype property of the constructor appears anywhere in the prototype chain of an object. The instanceof operator examines the presence of constructor.type in the object‘s prototype chain. The instanceof operator returns the boolean value that indicates if an object is an instance of the particular class.

Javascript Instanceof Operator

The instanceof operator is used to check the type of the object at a run time. The instanceof operator tests a presence of constructor.prototype in the object‘s prototype chain.

It checks the current object and returns true if the object is of the specified object type.

The Left Hand Side (LHS) operand is an actual object being tested to the Right Hand Side (RHS) operand, which is an actual constructor of a class.

#javascript #javascript instanceof #js

Javascript Instanceof Operator Example | Instanceof in Javascript

Javascript instanceof is an inbuilt operator that tests whether a prototype property of the constructor appears anywhere in the prototype chain of an object. The instanceof operator examines the presence of constructor.type in the object‘s prototype chain. The instanceof operator returns the boolean value that indicates if an object is an instance of the particular class.

Javascript Instanceof Operator

The instanceof operator is used to check the type of the object at a run time. The instanceof operator tests a presence of constructor.prototype in the object‘s prototype chain.

It checks the current object and returns true if the object is of the specified object type.

The Left Hand Side (LHS) operand is an actual object being tested to the Right Hand Side (RHS) operand, which is an actual constructor of a class.

See the following syntax.

object instanceof constructor

The object is to be tested, and the constructor is the function to test against.

#javascript #javascript instanceof #js

Rahul Jangid

1622207074

What is JavaScript - Stackfindover - Blog

Who invented JavaScript, how it works, as we have given information about Programming language in our previous article ( What is PHP ), but today we will talk about what is JavaScript, why JavaScript is used The Answers to all such questions and much other information about JavaScript, you are going to get here today. Hope this information will work for you.

Who invented JavaScript?

JavaScript language was invented by Brendan Eich in 1995. JavaScript is inspired by Java Programming Language. The first name of JavaScript was Mocha which was named by Marc Andreessen, Marc Andreessen is the founder of Netscape and in the same year Mocha was renamed LiveScript, and later in December 1995, it was renamed JavaScript which is still in trend.

What is JavaScript?

JavaScript is a client-side scripting language used with HTML (Hypertext Markup Language). JavaScript is an Interpreted / Oriented language called JS in programming language JavaScript code can be run on any normal web browser. To run the code of JavaScript, we have to enable JavaScript of Web Browser. But some web browsers already have JavaScript enabled.

Today almost all websites are using it as web technology, mind is that there is maximum scope in JavaScript in the coming time, so if you want to become a programmer, then you can be very beneficial to learn JavaScript.

JavaScript Hello World Program

In JavaScript, ‘document.write‘ is used to represent a string on a browser.

<script type="text/javascript">
	document.write("Hello World!");
</script>

How to comment JavaScript code?

  • For single line comment in JavaScript we have to use // (double slashes)
  • For multiple line comments we have to use / * – – * /
<script type="text/javascript">

//single line comment

/* document.write("Hello"); */

</script>

Advantages and Disadvantages of JavaScript

#javascript #javascript code #javascript hello world #what is javascript #who invented javascript