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...
If the variable is not defined, typeof will return the string “undefined”. Here’s how you can use it: let myVar; if (typeof myVar === "undefined") { console.log("myVar is undefined"); } else { console.log("myVar is defined"); } Output: myVar is undefined In this example...
// 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...
code inside yourif(myVar) { code }will be NOT executed only whenmyVaris equal to:false, 0, "", null, undefined, NaNor you never defined variablemyVar(then additionally code stop execution and throw exception). code inside yourif(myVar !== null) {code}will be NOT executed only whenmyVa...
When the variable is undefined, it means the variable is not declared. Users cant use it in the if-else conditional statement like the above method.To check the type of the undeclared variables, we can use the typeof operator. The typeof operator takes the variable as an operand and ...
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.');} ...
To check if a variable is an array in Javascript is essential to handle data appropriately. We will discuss three different approaches to check if a variable is an array or not. We are having an array and a string, and our task is to check if a variable is an array in JavaScript. ...
if(window['varname'] != undefined)// Global scope if(window['varname'] != void 0)// Old browsers If you know the variable exists but don't know if there's any value stored in it: 1 2 if(undefined != yourvar) if(void 0 != yourvar)// for older browsers ...
JavaScript Define a Function to Check If a Variable is a String 6 7 8 9 // Defining a function 10 function isString(myVar) { 11 return (typeof myVar === 'string'); 12 } 13 14 // Sample variables 15 var x = 10; 16 var y = true; 17 var z = "...
Javascript Boolean Type Introduction Using the typeof operator, we can check the datatype of a variable. If the variable is a Boolean value, typeof will return the string 'boolean'. Copy vara =Boolean(true);varb = false;//www.java2s.comvarc ="";vard = newDate();if(typeofa ==='...