How to Check for "undefined" in JavaScript?

The problem with undefined is that it can often be a lot trickier to find and fix than other errors. Everyone knows how to spot a null value, or an undefined variable, but finding undefined itself is more difficult. If you're in the market for some solid code, the below code checks are sure to help make sure that your function calls are returning data:

javascript check for undefined

By

Grepper on Jul 22, 2019

if (typeof myVariable === 'undefined'){
    //myVariable is undefined
}

15

javascript if undefined

By

Tame Toucan on Mar 25, 2020

if(typeof comment === 'undefined') {

  alert('Variable "comment" is undefined.');

} else if(comment === null){

  alert('Variable "comment" is null.');

}

Source: www.tutorialrepublic.com

7

test if is undefined javascript

By

experimental on Aug 10, 2020

let id;

if(typeof id === 'undefined') {
    console.log("id is undefined...");
}

1

js check if undefined

By

Prickly Peafowl on Jul 15, 2020

let foo = undefined
//will return true
typeof foo === 'undefined'

2

javascript check undefined

By

Batman on Jul 30, 2020

if(myVar === null) {
	console.log("Element is undefined");
}

8

undefined javascript check

By

Duco Defiant Dogfish on Mar 30, 2020

if(undefinedElement === null) {
	console.log("Element is undefined");
}

-1

Different methods are used to check for null or undefined in JavaScript, You can check for a single variable by using the "typeof" operator or "instanceof", You can also use "default value" as a condition to do something while checking

Javascript answers related to "javascript check undefined"

javascript check undefined javascript check undefined javascript check undefined javascript check undefined or null javascript check undefined or null javascript check undefined or null javascript null or empty javascript check undefined javascript check undefined javascript check undefined or null javascript check undefined remove undefined from array javascript check undefined or null check if value is a string javascript js palindrome number js palindrome number js string contains empty string in javascript isnumber javascript isNaN null undefined null undefined js this returns undefined javascript resize event how to check if object is empty javascript check if all elements in array are true javascript check if checkbox is checked javascript how to check whether a string contains a substring in typescript online javascript check undefined or null typescript check if object has key

View All Javascript queries

Javascript queries related to "javascript check undefined"

javascript check undefined javascript check undefined or null react router dom props.history is undefined react router dom return undefined ReactElement Function lacks ending return statement and return type does not include 'undefined'. reactjs TypeError: b is undefined vue is undefined vue 3 vue.use node js TypeError [ERR_INVALID_ARG_TYPE]: The argument must be of type string. Received undefined TypeError: Cannot read property 'name' of undefined ionic Uncaught TypeError: Cannot read property 'addEventListener' of undefined Cannot read property 'classList' of undefined js this returns undefined null undefined remove undefined from array trim undefined keys from object typescript how to check if object is empty javascript javascript check if string is number check online status javascript check if all elements in array are true javascript javascript check if array is in array check if checkbox is checked javascript check if value is a string javascript how to check if a string is an integer javascript javascript check if file exists in folder javascript check if json object is valid javascript check string sort ascending angular how to check previous route eslint version check in react how to check if bottom tab is active in react native material bottom tab how to check reactjs version in command prompt platform check in react native for status bar color node js to check 32 bit js check if image url exists check if date equal js check cookies client side ckeditor check if empty how to check if json data is received in ajax response js check if function is available in scope How to check checked checkbox in jquery How check the selected value in dropdown? typescript check if object has key how to check whether a string contains a substring in typescript online check if substring in string typescript how to check is value exists in array How to check angular version in project passing argument to function handler functional compoent javascript react reactjs javascript is mobile and desktop use javascript library in react node js send javascript javascript queryselectorall math.random javascript javascript onclick href location javascript get last element of array remove attribute javascript Javascript stop setInterval javascript round 2 decimals javascript to integer parse integer javascript javascript convert string to number Javascript write to text file afficher un div qui etait cache en javascript javascript in viewport javascript remove first character from string document ready javascript vanilla how to convert minutes into seconds in javascript how to get all elements with same class in javascript application/x-www-form-urlencoded javascript fetch add 10 seconds to date javascript javascript get random floating number how to remove duplicate array object in javascript Array unique values javascript remove element from array javascript to pascal case javascript javascript multiline string window onload javascript document ready javascript math floor javascript null read file javascript javascript urlencode json How to get current timestamp in javascript convert milliseconds to minutes and seconds javascript javascript object to json javascript startswith javascript reverse array regex space javascript javascript object entries timestamp to date javascript array length javascript javascript classlist add javascript object destructuring javascript first letter uppercase datetime to date javascript create element javascript foreach object javascript javascript redirection how to use javascript to get full file path default in javascript javascript get stack trace javascript show stack trace javascript style an element javascript convert array to object javascript object to array javascript merge objects Javascript merge two objects javascript and operator javascript replace spaces with nbsp window.open javascript auto close javascript sort array of date string.find javascript math.max in javascript javascript iterate through for loop javascript prototype explained javascript background color how to change image source using javascript how to get nth fibonacci javascript how to print a line in javascript javascript add css file add value to array javascript for array javascript javascript template literals javascript round to 2 decimal delete element from list javascript switch statement javascript javascript send post data with ajax generate random number array javascript from principal array add css in javascript set focus on input field javascript limit characters display javascript add an element to an array javascript javascript resize event javascript format price javascript new line javascript mouse up mouse down how to convert an array into an object using javascript change index array javascript javascript get array min and max javascript create array of objects with map sum all elements in array javascript get year javascript copyright draw rectangle on canvas javascript filter javascript array get data attribute javascript javascript if shorthand queryselector javascript generate random ip address javascript javascript date format mm/dd/yyyy hasownproperty javascript convert string to integer javascript addeventlistener javascript multiple functions javascript if not javascript date format dd-mm-yyyy string length JavaScript arrow function javascript download file javascript javascript event listener html to pdf javascript convert date to timestamp javascript javascript download file for loop inside a for loop javascript get current date javascript yyyy-mm-dd json to array javascript javascript array find iterate over array of objects javascript find a single element in array of objects javascript while javascript javascript addeventlistener javascript loop aray empty string in javascript interactive svg javascript make an object javascript where is select value in javascript event object javascript scrollleft stop how to stop requestanimationframe in javascript javascript add parameter to object javascript math.pow fetch method in javascript javascript change title validate latitude longitude javascript javascript integer length add object in array javascript to index using lodash Javascript pong game how to remove element from array in foreach javascript what is promise in javascript how to append item to an array in foreach javascript javascript add text to textarea overwrite javascript regex not in a set of characters convert pdf to base64 javascript and operator in javascript javascript math ceiling function javascript email validation javascript location.href how to reverse a string in javascript without using reverse method JavaScript Array Methods .reduce() hide automatically show and hide javascript get date format javascript using apis in javascript javascript truthy javascript algorithms

Browse Other Code Languages