Four ways to determine data type in JavaScript: typeof operator returns value type string instanceof operator checks whether it is an instance of the specified type Object.prototype.toString() method returns value type internal representation string Array. The isArray() method checks whether it is an array
Method to determine data type in JavaScript
In JavaScript, determine The data type has the following methods:
1. typeof operator
typeof
operator returns a string representing the given value type. Possible return values include:
-
"undefined"
: Undefined value. -
"null"
: Null value. -
"number"
: Number. -
"bigint"
: Big integer. -
"string"
:String. -
"boolean"
: Boolean value. -
"symbol"
: Symbol. -
"object"
: All other values such as objects, arrays, functions, etc.
Example:
console.log(typeof undefined); // "undefined" console.log(typeof null); // "object" console.log(typeof 42); // "number" console.log(typeof "hello"); // "string" console.log(typeof true); // "boolean" console.log(typeof [1, 2, 3]); // "object"
2. instanceof operator
instanceof
operator Checks whether the given value is an instance of the specified type. It returns a Boolean value: true
for yes, false
for no.
Syntax:
object instanceof Constructor
Where:
-
object
is the value to be checked. -
Constructor
is the constructor or built-in type of the class to be checked.
Example:
console.log([] instanceof Array); // true console.log({} instanceof Object); // true console.log("hello" instanceof String); // false
3. Object.prototype.toString() method
Object The .prototype.toString()
method returns a string representing the internal representation of the given value type. It is usually represented in the following format:
<code>"[object Type]"</code>
where Type
is the type of the value.
Example:
console.log(Object.prototype.toString.call(undefined)); // "[object Undefined]" console.log(Object.prototype.toString.call(null)); // "[object Null]" console.log(Object.prototype.toString.call(42)); // "[object Number]" console.log(Object.prototype.toString.call("hello")); // "[object String]" console.log(Object.prototype.toString.call(true)); // "[object Boolean]" console.log(Object.prototype.toString.call([1, 2, 3])); // "[object Array]"
4. Array.isArray() method
Array.isArray()
Method specifically checks whether the given value is an array. It returns a Boolean value: true
for yes, false
for no.
Example:
console.log(Array.isArray([])); // true console.log(Array.isArray({})); // false
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