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...
Ensure the value is notundefinedornullusingArray.prototype.includes(). Compare theconstructorproperty on the value withtypeto check if the provided value is of the specifiedtype. constis=(type,val)=>![,null].includes(val)&&val.constructor===type;// Examplesis(Array,[1]);// trueis(ArrayBuff...
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 ...
Sometime you need to check one prop exists on the object and value should not be ´null´ or ´undefined´. One problem people may occur with: const{get} = require('lodash')constobj = {a:123}constexisting =typeofget(obj,'a') !== undefined//true Here we missed if the value...
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...
Thetypeofoperator can additionally be used alongside the===operator to check if the type of a variable is equal to'undefined'or'null': leta;if(typeofa ==='undefined') {console.log('Undefined variable'); }elseif(typeofa ==='null') {console.log('Null-value'); } ...
Now to check whether a given variable is a string or not, we'll use a JavaScript operator calledtypeof. Syntax: typeof variable; This operator returns the data type of the variable specified after it. If the variable is of string data type, it will return a string. ...
//code to check if a value exists in an array using includes function array.includes('hello'); // true array.includes(300); // true array.includes(0); // true array.includes(undefined); // true array.includes(null); // true array.includes(symbol); // true ...
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 find that it is indeed “undefined”. This method is particularly useful because it won’t throw an error even if the variable hasn’t been declare...
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...