The meaning of typeof in js

The typeof operator is used to determine the type of a variable or expression in JavaScript and returns one of the following string values: "undefined": The variable is undefined or the value is undefined "boolean": The variable is a Boolean value "number": The variable is a number "string": The variable is a string "object": The variable is an object "function": The variable is a function "symbol": The variable is a Symbol type (ES6) "bigint": The variable is a BigInt type (ES2020 )

typeof means in JavaScript

In JavaScript, typeof operator Used to determine the type of a variable or expression. It returns a string representing the type of variable or expression.

Usage:

typeof variable_or_expression;

Where, variable_or_expression can be any valid JavaScript variable or expression.

Possible return values:

typeof The operator can return the following string values:

• "undefined " - When the variable is undefined or has the value undefined.
• "boolean" - When the variable is a boolean (true or false).
• "number" - when the variable is a number.
• "string" - when the variable is a string.
• "object" - when the variable is an object.
• "function" - when the variable is a function.
• "symbol" - when the variable is of type Symbol (introduced in ES6).
• "bigint" - when the variable is of type BigInt (introduced in ES2020).

Example:

console.log(typeof undefined); // "undefined"
console.log(typeof true); // "boolean"
console.log(typeof 42); // "number"
console.log(typeof "hello world"); // "string"
console.log(typeof {}); // "object"
console.log(typeof function() {}); // "function"
console.log(typeof Symbol()); // "symbol"
console.log(typeof 123n); // "bigint"

typeof The operator can be used to check the type of a variable and perform different operations based on the type. For example, the following code block checks whether the variable x is a number, and if so, adds 1 to x:

const x = 42;

if (typeof x === "number") {
  x++;
}

console.log(x); // 43

The above is the detailed content of The meaning of typeof in js. For more information, please follow other related articles on the PHP Chinese website!