https://stackoverflow.com › questions › 2647867
How can I determine if a variable is 'undefined' or 'null'?if( typeof variable === 'undefined' || variable === null ){ // Do stuff } This should work for any variable that is either undeclared or declared and explicitly set to null or undefined. The boolean expression should evaluate to false for any declared variable that has an actual non-null value.
https://stackoverflow.com › questions › 3390396
How can I check for "undefined" in JavaScript? - Stack OverflowIf you are interested in knowing whether the variable hasn't been declared or has the value undefined, then use the typeof operator, which is guaranteed to return a string: if (typeof myVar !== 'undefined') Direct comparisons against undefined are troublesome as undefined can be overwritten. window.undefined = "foo";
https://www.freecodecamp.org › news › javascript-check-if-undefined-how-to-test-for...
JavaScript Check if Undefined – How to Test for Undefined in JSHow to Check if a Variable is Undefined in JavaScript with Direct Comparison. One of the first methods that comes to mind is direct comparison. This is where you compare the output to see if it returns undefined. You can easily do this in the following way: let user = { name: "John Doe", age: 14 . }; if (user.hobby === undefined) {
https://masteringjs.io › tutorials › fundamentals › undefined-check
How to Check if a JavaScript Variable is UndefinedWhen using x === undefined, JavaScript checks if x is a declared variable that is strictly equal to undefined. If you want to check if x is strictly equal to undefined regardless of whether is has been declared or not, you should use typeof x === 'undefined'.
https://stackabuse.com › javascript-check-if-variable-is-a-undefined-or-null
JavaScript: Check if Variable is undefined or null - Stack AbuseIn this short guide, you'll learn how to check if a variable is undefined, null or nil in vanilla JavaScript and with Lodash - with practical examples and advice on when to use which approach.
https://www.delftstack.com › fr › howto › javascript › javascript-undefined
Vérifier si une variable n'est pas définie dans JavaScriptUtilisez l’opérateur typeof pour vérifier l’indéfini en JavaScript. Ce didacticiel explique comment vérifier si une variable n’est pas définie dans JavaScript. Une variable est dite undefined si elle est déclarée sans se voir attribuer une valeur initiale.
https://attacomsian.com › blog › javascript-check-if-variable-is-undefined-or-null
How to check if a variable is undefined or NULL in JavaScriptTo check if a variable is undefined or null in JavaScript, either use the equality operator == or strict equality operator ===. In JavaScript, a variable is considered undefined if it is declared but not assigned a value.
https://ui.dev › check-for-undefined-javascript
How to check for undefined in JavaScript - ui.devThe way I recommend to check for undefined in JavaScript is using the strict equality operator, ===, and comparing it to the primitive undefined. Checking for `undefined`` this way will work in every use case except for one, if the variable hasn't been declared yet.
https://www.golinuxcloud.com › javascript-check-if-undefined
How to check if undefined in JavaScript? [SOLVED] - GoLinuxCloudThere are different ways to check if a variable is undefined in JavaScript, including using the typeof operator, the comparison operator (===) with the value undefined, or the use of the ternary operator.
https://codedamn.com › news › javascript › check-if-undefined-null
How to check if value is undefined or null in JavaScript - codedamnIf you want to check if a value is specifically undefined or null without type coercion, you can use the identity operator (===). The identity operator checks for both value and type equality, which means it does not perform type coercion.
