Here is an example of the code. let a; console.log(typeof a === 'undefined'); // true This method is safe because it won’t throw an error if the variable is undeclared. 2. Using Strict Equality (===) Strict equality (===) can also be used to check if a variable is ...
In the above example, we have used the first if statement to check if the "a" variable is either undefined or null. If it satisfies either of the conditions, then the if block will execute; otherwise, the else block will execute. In the second statement, we have used the if statement ...
let someVariable = 'Hello!' if (typeof somevariable === 'undefined') { console.log('Undefined variable'); } else if (typeof somevariable === 'null') { console.log('Null-value'); } else { console.log(somevariable); } Here, we're trying to check whether someVariable is null ...
Directly Compare a Variable Withundefinedto Check Undefined in JavaScript varx;if(x===undefined){text='x is undefined';}else{text='x is defined';}console.log(text); Output: "x is undefined" Here we take an undefined variable name and compare it directly withundefinedwithout using any funct...
In JavaScript, the typeof operator is the most used method to check the type of any variable. Alternatively, you can use the typeof() method: let myString = 'John Doe'; typeof myString; // string typeof(myString); // string If used with a string, the typeof operator returns "...
Variable Scope Solution 2: We can use typeofoperatorto check the variable is defined or not. if (typeof variable !== 'undefined') { // the variable is defined } Solution 3: You can use this code: if (typeof variable === 'undefined') { // variable is undefined } ...
If you want to check whether a variable has been initialized or defined (i.e. test whether a variable has been declared and assigned a value) you can use the typeof operator.The most important reason of using the typeof operator is that it does not throw the ReferenceError if the ...
Here's a Code Recipe to check whether a variable or value is either an array or not. You can use the Array.isArray() method. For older browser, you can use the polyfill 👍 constvariable=['🍝','🍜','🍲'];// ✅ NEWER BROWSERArray.isArray(variable);// 🕰 OLDER BROWSERObj...
A function to check a cookie value A Function to Set a Cookie First, we create afunctionthat stores the name of the visitor in a cookie variable: Example functionsetCookie(cname, cvalue, exdays) { constd =newDate(); d.setTime(d.getTime() + (exdays*24*60*60*1000)); ...
("Caching is:"+(this.myConfig.useCaching)?"enabled":"disabled");},// 重写当前的配置(configuration)myMethod3:function(newConfig){if(typeofnewConfig==="object"){this.myConfig=newConfig;console.log(this.myConfig.language);}}};myModule.myMethod();// Where in the world is Paul Irish ...