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JavaScript – typeof Operator ”; Previous Next The typeof Operator The typeof operator in JavaScript is a unary operator used to get the data type of a particular variable. It is placed before its single operand, which can be of any type. Its returns a string value indicating the data type of its operand. JavaScript contains primitive and non-primitive data types. There are seven primitive or basic in JavaScript data types – number, string, boolean, undefined, null, symbol, and bigint. There is also a composite data type called object. The object data type contains three sub data type – Object, Array and Date. Syntax Following is the syntax of the typeof operator − typeof (operand); We can write the operand without parenthesis as follows − typeof operand; Parameter operand − It can be a value, variable or expression representing the object or primitive. In JavaScript, primitives are data that are not object and have no methods or properties. Return Value It returns the string value representing the data type of the operand. Datatypes Returned by typeof Operator Here is a list of the return values for the typeof Operator. Type String Returned by typeof Number “number” String “string” Boolean “boolean” Object “object” Function “function” Undefined “undefined” Null “object” Symbol “symbol” Bigint “bigint” There are seven primitive datatypes in JavaScript – number, string, boolean, bigint, undefined, null, and symbol. The typeof operator is useful to identify these primitive or basic datatypes. The typeof operator returns same datatype of the all primitive values except the null. It returns “object” for the null values. For object, date and array it returns “object” as datatype. For functions and classes, it returns “function” as datatype. Let”s use the typeof operator to identify these datatypes one by one. typeof 10; // returns ”number” typeof ”Hello World”; // returns ”string” typeof true; // returns ”boolean” typeof {name:”Tutorialspoint”}; // returns ”object” typeof function foo(){};// returns ”function” typeof undefined; // returns ”undefined” typeof null; // returns ”object” typeof Symbol(); // returns ”symbol” typeof 10n; // returns ”bigint” JavaScript typeof Operator to Check Number Type In JavaScript, number type represents numeric values. JavaScript uses a floating-point representation for all numbers. The JavaScript typeof operator returns ”number” for all types of numbers such as integers, floating points, zero, Infinity, NaN etc. typeof 10; //returns “number”; typeof -10; //returns “number”; typeof 0; //returns “number”; typeof 10.20; //returns “number”; typeof Math.LN10; //returns “number”; typeof Infinity; //returns “number”; typeof NaN; //returns “number”; typeof Number(”1”); //returns “number”; typeof Number(”hello”); //returns “number”; Example The example below demonstrates how to use the typeof operator to check number data types. <html> <body> <p> Using typeof operator to check number data type </p> <div id=”output”></div> <script> let num = 42; document.getElementById(“output”).innerHTML = typeof num; </script> <p>Set the variable to different value and then try…</p> </body> </html> Output Using typeof operator to check number data type number Set the variable to different value and then try… JavaScript typeof Operator to Check String Type Strings represent sequences of characters. The typeof operator helps identify string variables. The JavaScript typeof operator returns “string” for all type of strings, such as empty string, string of characters, string words, multiline string etc. typeof “10”; //returns “string”; typeof “”; //returns “string”; typeof “Hello World”; //returns “string”; typeof String(10); //returns “string”; typeof typeof 2; //returns “string”; Example In the example below we use typeof operator to check string datatype. <html> <body> <div id=”output”></div> <script> let str = “Hello World”; document.getElementById(“output”).innerHTML = typeof str; </script> <p>Set the variable to different value and then try…</p> </body> </html> Output string Set the variable to different value and then try… JavaScript typeof Operator to Check Boolean Type The boolean values represent true or false. The tyepof operand returns boolean for boolean variables. typeof true; //returns “boolean”; typeof false; //returns “boolean”; typeof Boolean(10); //returns “boolean”; Example In the example below, we use typeof operator to check boolean datatype. <html> <body> <div id=”output”></div> <script> let bool = true; document.getElementById(“output”).innerHTML = typeof bool; </script> <p>Set the variable to different value and then try…</p> </body> </html> Output boolean Set the variable to different value and then try… JavaScript typeof Operator to Check Symbol Type Symbols were introduced in ES6 and provide a way to create unique identifiers. Using typeof operator with symbols returns “symbol”. typeof Symbol(); //returns “symbol”; typeof Symbol(“unique values”); //returns “symbol”; Example In the example below, we use typeof operator to check Symbol datatype. <html> <body> <div id=”output”></div> <script> let sym = Symbol(“Hello”); document.getElementById(“output”).innerHTML = typeof sym; </script> <p>Set the variable to different value and then try…</p> </body> </html> Output symbol Set the variable to different value and then try… JavaScript typeof Operator to Check Undefined and Null The “undefined” type represents a lack of a value. The “null” type represents the absence of any object value. When using typeof operator with an undefined variable, it returns ”undefined”. Surprisingly, using typeof operator with null also returns “object”, which is a known quirk in JavaScript. typeof undefined; //returns “undefined”; typeof null; //returns “object”; Please note typeof operator will return “undefined” for both undeclared variable and declared but unassigned variables. Example In the example below, we use typeof operator to check undefined datatype. <html> <body> <div id=”output”></div> <script> let x; document.getElementById(“output”).innerHTML = typeof x; </script> <p>Set the variable to different value and then try…</p> </body> </html> Output undefined Set the variable to different value and then try… JavaScript typeof Operator to Check Object Type The JavaScript typeof operator returns “object” for all types of object such as JavaScript objects, arrays, dates, regex, etc. const obj = {age: 23}; typeof obj; //returns “object”; const arr = [1,2,3,4]; typeof arr; //returns “object”; typeof new Date(); //returns “object”; typeof new String(“Hello World”); //returns “object”; Example In the example below, we use typeof operator to check object datatype. <html> <body> <div id=”output”></div> <script> const person = {name: “John”, age: 34}; document.getElementById(“output”).innerHTML = typeof person; </script> <p>Set the variable to different value and then try…</p> </body> </html> Output object Set the variable to different value