JavaScript typeof is a built-in operator that returns a data type of its operand as a string. The operand can be any object, function, or variable.
Syntax
typeof operand
// OR
typeof (operand)
Example 1: typeof String
The operand parameter represents the object or primitive whose type will be returned.
console.log(typeof 'appdividend');
Output
Example 2: typeof Number
We can also check the Number as well.
let appInt = 21;
console.log(typeof (appInt));
It will return the Number.
Next, let’s check the object.
const obj = {
name: 'krunal',
age: 26
};
console.log(typeof (obj));
Output
Example 3: typeof and === operator.
We can compare the variable’s datatype using the typeof operator and get the result as true or false.
console.log(typeof 'appdividend' === 'string');
Output
We can do the same for the Number and other data types.
console.log(typeof 21 === 'number');
We get true; if the data type does not match, it will return false.
Example 4: typeof undefined
In JavaScript, the variable without any value has the value undefined. Therefore, the type is also undefined.
let jet;
console.log(typeof (jet));
Output
Example 5: typeof null
The null is an exception to JavaScript since the beginning.
console.log(typeof null === 'object');
The output is true. That means JavaScript counts null as an object.
Since starting, JavaScript values were represented as the type tag and a value. The type tag for objects was 0. The null was described as the NULL pointer (0x00 in most platforms).
Consequently, the null had 0 as the type tag, hence the “object” typeof return value.
Example 6: typeof NaN
The type of NaN, which stands for Not a Number, is, surprisingly, a number. This is because, in computing, NaN is technically a numeric data type.
console.log(typeof NaN);
Output
number
However, it is the numeric data type whose value cannot be represented using the actual numbers.
This also explains why not all NaN values are equal.
const x = NaN;
const y = NaN;
console.log(x === y);
Output
false
Example 7: typeof array
The typeof an array is an object. In JavaScript, arrays are technical objects with certain behaviors and abilities.
let st3 = ['Eleven', 'Dustin', 'Lucas'];
console.log(typeof st3);
Output
object
We can differentiate an Array object from an Object object using the Array.isArray() method.
Example 8: typeof class
console.log(typeof class Foo { });
Output
function
Conclusion
To check a data type of a variable in JavaScript, you can use the typeof operator. For example, typeof 21 returns “Number” and typeof khushi returns “String”.
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