Unable to get property undefined or null reference

This is a JavaScript error arises when JavaScript/jQuery is not able to refer to the element that happened while your browser was loading the page. In some cases, reloading the page should resolve the issue and allow the items to load in the proper order. If this continues, refer the following solution.
Javascript undefined or null reference

You have tried to use a variable, property, or a method return value but it contains null or undefined - which means that there is no instance of a class in the variable. If you are getting data for object from an async call(API's), these kind of problems will arise. So you should always check the object whether it is null or undefined then if it is not, you can access its properties.

The standard way to catch null and undefined simultaneously is this:

if (variable == null) { // write your code here. }

Because, null == undefined is true, the above code will catch both null and undefined.

Also you can write equivalent to more explicit but less concise:

if (variable === undefined variable === null) { // write your code here. }

This should work for any variable that is either undeclared or declared and explicitly set to null or undefined .

getElementById()

In most cases this error is related to getElementById() . You need to find the element you want to get the value of first. It's not quite like a server side language where you can type in an object's reference name and a period to get or assign values. So getting a value from an input could look like this:

var value = document.getElementById("frm_request").value

Also you can use some JavaScript Framework , e.g. jQuery, which simplifies operations with Document Object Model (DOM) and also hides differences between various browsers from you. Getting a value from an input using jQuery would look like this:

var value = $("#element).value //input with ID var value = $(".element).value //input with class

null Vs undefined in JavaScript

undefined means a variable has been declared but has not yet been assigned a value, such as:

var myVar; alert(myVar); //shows undefined alert(typeof myVar); //shows undefined

null is an assignment value. It can be assigned to a variable as a representation of no value:

var myVar = null; alert(myVar); //shows null alert(typeof myVar); //shows object

Next : SyntaxError: Cannot use import statement outside a module

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