JavaScript is a loosely typed language which means you don't specify the data type of a variable while declaring it.
let x;
A variable in JavaScript can take any value. Suppose you have assigned a number to a variable and then later on in the code, you have assigned a string to that same variable. In that case, JavaScript won't give any errors.
let pi = 3.14; pi = "Pie"; console.log(pi); //"Pie"
It is important for you to know the type of value stored in a variable. For this, JavaScript provides the typeof operator. The typeof operator is a unary operator mainly used to check the data type of a variable or value.
The following table shows the value returned by the typeof operator for any JavaScript value:
| Value | typeof value |
|---|---|
| Number such as 3.14, 10, etc. | "number" |
| Boolean such as true or false | "boolean" |
| String such as "Pizza", "Burger", etc. | "string" |
| Function such as function sum(a,b){return a+b} | "function" |
| Array such as [11,22,33,44] | "object" |
| Object such as {name: 'Mohit Natani'} | "object" |
| Any instance of a class | "object" |
| null | "object" |
| undefined | "undefined" |
| BigInt | "bigint" |
| Symbol | "symbol" |
In JavaScript, object, array, map, set, and instances of a class are called reference variables. So, when you use the typeof operator with a reference variable, the typeof operator returns "object". To check which class a reference variable belongs to, use the instanceof operator.
Let's see some examples that show you how to use the typeof operator in JavaScript.
const PI = 3.14;
let food = "Pizza",
arr = [11,22,33,44],
boolean = false,
pdt = {
name: 'Blue Flared Jeans',
price: 1199
};
function sum(a, b){
return a + b;
}
console.log(typeof PI); //"number"
console.log(typeof food); //"string"
console.log(typeof arr); //"object"
console.log(typeof boolean); //"boolean"
console.log(typeof pdt); //"object"
console.log(typeof sum); //"function"
You mainly use the typeof operator in an if statement to check whether a variable is of a particular type or not. For example, you can check whether a variable is a string or not by running the following code:
let food = "Pizza";
if(typeof food === "string"){
console.log("Variable food is a string.");
}else{
console.log("Variable food is not a string.");
}
Output
"Variable food is a string."
