In JavaScript, there are various methods available to check if a variable is undefined. Each method has its own use cases and subtle differences. 1. Using typeof Operator The typeof operator can be used to check
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Topic: JavaScript / jQueryPrev|NextAnswer: Use the typeof operatorIf 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....
JavaScript, in turn, decides the data type of the variable, later, depending on the values assigned to these variables. It is seemingly easy to determine the data type of a variable. But some scenarios can put us in a fix. Especially in the case of values returned by the REST API ...
Second, no, they are not directly equivalent. If you really want to check for null, do: 1 2 if(null== yourvar)// with casting if(null=== yourvar)// without casting If you want to check if a variable exist 1 2 3 if(typeofyourvar !='undefined')// Any scope ...
function func1(){ }; function func2(){ }; var f1 = new func1(); f1 instanceof func1; //returns true f1 instanceof func1; //returns false f1 instanceof Object; //returns true Try it Please note that the instanceof operator returns "true" if a variable is initialized with the "...
Method 1: Using the typeof Operator One of the simplest ways to check if a variable is undefined is by using the typeof operator. This operator returns a string that indicates the type of the unevaluated operand. If the variable is not defined, typeof will return the string “undefined”...
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...
// Sample variablevarmyVar='Hello';// Test if variable is a stringif(typeofmyVar==='string'){alert('It is a string.');}else{alert('It is not a string.');} You can also define a custom function to check whether a variable is a string or not. ...
{ "compilerOptions": { "outFile": "../../built/local/tsc.js", "checkJs": true, "allowJs": true }, "include": [ "src/*" ], "exclude": [ "node_modules", ] }Now, VS Code can point out type errors in our JavaScript code....