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typeof Operator in JavaScript

In JavaScript, the typeof operator is used to determine the type of a value. It is often used when you want to check the type of a variable or a value before performing an operation on it.

Syntax​

The syntax of the typeof operator is as follows:

app.js
typeof value
  • The typeof operator is followed by the value whose type you want to determine.
  • The value can be a variable, a literal, or an expression.
  • The typeof operator returns a string that represents the type of the value.
  • The returned string can be one of the following values:
    • "undefined": If the value is undefined.
    • "boolean": If the value is a boolean.
    • "number": If the value is a number.
    • "string": If the value is a string.
    • "symbol": If the value is a symbol.
    • "function": If the value is a function.
    • "object": If the value is an object or null.
    • "bigint": If the value is a BigInt.
    • "object": If the value is an object or null.

Example​

The following example demonstrates how to use the typeof operator to determine the type of a value:

app.js
const name = "John";
const age = 30;
const isMarried = false;
const fruits = ["apple", "banana", "cherry"];
const person = {
  name: "John",
  age: 30,
};

console.log(typeof name); // string
console.log(typeof age); // number
console.log(typeof isMarried); // boolean
console.log(typeof fruits); // object
console.log(typeof person); // object
console.log(typeof undefinedVariable); // undefined
console.log(typeof nullVariable); // object
  • In this example, we have used the typeof operator to determine the type of different values such as strings, numbers, booleans, arrays, objects, undefined, and null.
  • The typeof operator returns the type of the value as a string.
  • The typeof operator is often used to check the type of a value before performing an operation on it, such as type conversion or type-specific operations.
  • The typeof operator is useful when you want to handle different types of values differently in your code.
  • The typeof operator can be used to determine the type of a variable or a value at runtime, which can be useful in dynamic programming scenarios.
  • The typeof operator can be used to determine the type of a value before performing an operation on it, such as type conversion or type-specific operations.
  • The typeof operator can be used to handle different types of values differently in your code.
  • The typeof operator can be used to determine the type of a variable or a value at runtime, which can be useful in dynamic programming scenarios.
  • The typeof operator can be used to determine the type of a value before performing an operation on it, such as type conversion or type-specific operations.

Using the typeof Operator with Functions​

The typeof operator can be used to determine the type of a function. It returns "function" if the value is a function.

app.js
function greet() {
  console.log("Hello, World!");
}

console.log(typeof greet); // function
  • In this example, we have used the typeof operator to determine the type of the greet function.
  • The typeof operator returns "function" because the greet value is a function.
  • The typeof operator can be used to determine the type of a function, which can be useful when you want to handle functions differently in your code.
  • The typeof operator can be used to determine the type of a function at runtime, which can be useful in dynamic programming scenarios.
  • The typeof operator can be used to determine the type of a function before performing an operation on it, such as calling the function or passing it as an argument to another function.
  • The typeof operator can be used to handle functions differently in your code based on their type.

Using the typeof Operator with null​

The typeof operator returns "object" if the value is null. This is a historical bug in JavaScript, and it is not expected to change.

app.js
const person = null;

console.log(typeof person); // object

In this example, we have used the typeof operator to determine the type of the person value, which is null. The typeof operator returns "object" because the person value is null.

The typeof operator returns "object" if the value is null. This is a historical bug in JavaScript, and it is not expected to change.

The typeof operator can be used to determine the type of a value at runtime, which can be useful in dynamic programming scenarios.

The typeof operator can be used to determine the type of a value before performing an operation on it, such as type conversion or type-specific operations.

Using the typeof Operator with Symbols​

The typeof operator returns "symbol" if the value is a symbol.

app.js
const symbol = Symbol("mySymbol");

console.log(typeof symbol); // symbol
  • In this example, we have used the typeof operator to determine the type of the symbol value, which is a symbol.
  • The typeof operator returns "symbol" because the symbol value is a symbol.
  • The typeof operator can be used to determine the type of a symbol, which can be useful when you want to handle symbols differently in your code.
  • The typeof operator can be used to determine the type of a symbol at runtime, which can be useful in dynamic programming scenarios.
  • The typeof operator can be used to determine the type of a symbol before performing an operation on it, such as type conversion or type-specific operations.
  • The typeof operator can be used to handle symbols differently in your code based on their type.
caution

The typeof operator returns "object" if the value is null. This is a historical bug in JavaScript, and it is not expected to change.

Conclusion​

In this tutorial, you learned about the typeof operator in JavaScript and how to use it to determine the type of a value. You also learned about the different types of values that the typeof operator can return, such as "undefined", "boolean", "number", "string", "symbol", "function", "object", and "bigint". You also learned about the historical bug in JavaScript where the typeof operator returns "object" for null values. The typeof operator is useful when you want to handle different types of values differently in your code, and it can be used to determine the type of a variable or a value at runtime, which can be useful in dynamic programming scenarios.