In JavaScript, undefined is the default value for variables that have been declared but not initialized. On the other hand, null is an intentional assignment that explicitly indicates the absence of a value. Methods to Check if a Variable is Undefined Using typeof Operator Using Strict Equality...
JavaScript can make it difficult to distinguish between different undefined values. Boolean operations also have a couple of gotchas you must be aware of when dealing withNaNvalues. There are situations where one has to check and see if a certain value is of typeNaN. As such, here are some...
When the value is absolutely not present in the variable or string or anything else, we call it as Undefined. In JavaScript, undefined is a one of the primitive data type. It is used to represent the absence of a value. It get assigned to a variable when it is declared but not ...
// Undefined variableleta;if(a ==null) {console.log('Null or undefined value!'); }else{console.log(a); } This would check whetheraiseithernullorundefined. Sinceaisundefined, this results in: Null or undefined value! Though, we don't really know which one of these is it. If we were...
let myVar; if (typeof myVar === "undefined") { console.log("myVar is undefined"); } else { console.log("myVar is defined"); } Output: myVar is undefined In this example, we declare a variable myVar without assigning any value to it. When we check its type using typeof, we ...
This is why it’s better to use thetypeofoperator to really check if a value isundefined. Thetypeofoperator won’t throw an error when you haven’t declared the variable during the checking, but a direct comparison such asy === undefinedwill break your JavaScript application. ...
In JavaScript, a value can either be a primitive or an object. Therefore, you can check if a value is a JavaScript primitive (as opposed to being an object) using the following check: !(value instanceof Object) You may see value !== Object(value) as a means to check for prim...
//code to check if a value exists in an array using javascript for loop var fruits_arr = ['Apple', 'Mango', 'Grapes', 'Orange', 'Fig', 'Cherry']; function checkValue(value, arr) { var status = 'Not exist'; for (var i = 0; i < arr.length; i++) { var name = arr[...
Alternatively, it can also be used astypeof()methodin JavaScript. Syntax: typeof(variable); Example 1: str="This is my place.";if(typeofstr==String){console.log('The variable is a String.');}else{console.log('The variable is not a String.');} ...
keys(value).length === 0 && value.constructor === Object; value = null; // null value = undefined; // undefined Perfect, no error is thrown 😁# B. Empty Object Check in Older BrowsersWhat if you need to support older browsers? Heck, who am I kidding! We all know when I say...