Ошибка cannot read properties of null reading result

Столкнулся с ошибкой

Сам код —

<script>
mult = function() {
    var second = document.getElementById('usdt1').value;
    document.getElementById('result').value = 42 * second;
    var second2 = document.getElementById('btc2').value;
    document.getElementById('result').value = 12000 * second2;
    var second3 = document.getElementById('eth3').value;
    document.getElementById('result').value = 120 * second3;
    var second4 = document.getElementById('ltc4').value;
    document.getElementById('result').value = 50 * second4;
    var second5 = document.getElementById('busd5').value;
    document.getElementById('result').value = 43 * second5;
    var second6 = document.getElementById('usdc6').value;
    document.getElementById('result').value = 44 * second6;
    var second7 = document.getElementById('dash7').value;
    document.getElementById('result').value = 746 * second7;
}
</script>

Помогите пожалуйста решить, мучаюсь очень долго.

задан 12 окт 2022 в 10:35

Int4s's user avatar

3

В приведённом ниже примере скрипт с атрибутом defer будет ожидать, когда все элементы DOM будут загружены, соответственно, если ошибки в id-элемента ошибки не будет, вы получите необходимое значение.

<head>
<script defer>
  var mult = function() {
    var second = document.getElementById('usdt1').value;
    document.getElementById('result').value = 42 * second;
    var second2 = document.getElementById('btc2').value;
    ....
  } 
</script> 
</head> 
<body>
  <input id="usdt1" type='text'></input>
  <input id="usdt2" type='text'></input>
</body>

Также, вы можете поместить скрипт в самый низ body, уже после создания всего дерева DOM.

ответ дан 12 окт 2022 в 12:47

Nickolai Bondarenko's user avatar

Источник

As a Javascript programmer, you must have dealt with the “TypeError: cannot read properties of null”. 

In JavaScript, sometimes your code works completely fine, or you can get trapped in errors. This standard error occurs when one tries to read a property or call a method on a null object. In simple words, you try to access the value of null or undefined. If you are still in the same confused state, read further to find a precise solution. 

Before we move toward the answer, let’s discuss two basic terms, null and DOM, in detail, which will help you to understand the article completely.

Table of Contents
  1. What is a Null in JavaScript?
  2. What is DOM in JavaScript?
  3. Causes of the “TypeError: Cannot Read Properties of Null” Error
  4. Ways to Fix the “TypeError: Cannot Read Properties of Null” Error

What is a Null in JavaScript?

In JavaScript, a null is a primitive value, meaning the intentional absence of any object value. It is treated as a false in boolean operations. A variable with a null value is of the object type. Now understand null with the help of an example:

Code

console.log("Example of null");

let a = null;

console.log("Type of a:" ,typeof a);

console.log("A contain:" ,a);

Output

Example of null

Type of a: object

a contain: null

What is DOM in JavaScript?

Dom stands for Document Object Model in JavaScript; it is a programming interface that allows us to select, create, modify or remove elements from a document. We can easily add events to our document elements to make our page more dynamic.

Causes of the “TypeError: Cannot Read Properties of Null” Error

Normally, we face TypeError: cannot read properties of null in JavaScript when we try to access a property of the null object. Here we have a list of the most common causes of this error which are:

  1. Write wrong spelling
  2. Access property of a null object
  3. Inserting script tags before DOM elements declaration

Cause 1: Write The Wrong Spelling

When we use the wrong spell of an element id, we face this error now; let’s see an example of where we found this error.

Code

<!DOCTYPE html>

<html lang="en">

  <head>

  </head>

  <body>

 

  <input type="text" id="fname" name="fname">

 <script>

var first_name = document.getElementById("name").value;

console.log(firstName)

</script>




  </body>

</html>

Output

TypeError: cannot read properties of null

In the above coding, we write fname and in the script tag, we are trying to get the id name which is not present; that’s why we face this error.

Cause 2: Accessing a Property of a Null Object

Whenever we try to access a property of a null object, we have to face the type error. Now see a simple example in which we explain this concept:

Code

console.log("Error due to Property of null");

let myvariable=null;

console.log("length of variable is:" ,myvariable.value);

Output

TypeError: cannot read properties of null

Cause 3: Inserting Script Tags Before Dom Element Declaration

The TypeError: cannot read properties of null is commonly occurs when we use the getElementById() method and pass it an id that is not present in the DOM. Usually, this error occurs when we write a script tag before the DOM element declaration. Now understand the reason for this error with the help of an example:

Code

Index.html

<!DOCTYPE html>

<html lang="en">

  <head>

  </head>

  <body>

  <script src="src/script.js"></script>

  <input type="text" id="name" name="name">

   

  </body>

</html>




Script.js

var firstName = document.getElementById("name").value;

console.log(firstName)

Output

TypeError: cannot read properties of null

In this code, we write script tags before declaring DOM elements; that’s why we have TypeError.

Ways to Fix the “TypeError: Cannot Read Properties of Null” Error

Following are some solutions we can use to fix TypeError: cannot read properties of null in JavaScript.

  1. Check element id
  2. Write script tag after DOM elements declared
  3. Ways to handle null values
  4. Check if The Object Is Null or Undefined
  5. Check for Typo Errors
  6. Check if the object and property exist
  7. Use Type Checking

Now have a look at the solutions to that errors.

Solution 1: Check Element Id

It’s a good practice to always double-check the element id so you save yourself from this common type of error. Now solve the above error by simply writing the correct element id.

Code

<!DOCTYPE html>

<html lang="en">

  <head>

  </head>

  <body>

 Enter your First Name:

  <input type="text" id="fname" name="fname">

 <script>

var first_name = document.getElementById("fname").value;

</script>




  </body>

</html>

Output

TypeError: cannot read properties of null

Solution 2: Write Script Tag After DOM Elements Declaration

Always try to write a script tag at the end of the body tag or after the DOM element declaration. Now understand this solution by removing the error from the above example:

Code

Index.html

<!DOCTYPE html>

<html lang="en">

  <head>

  </head>

  <body>

 Enter your First Name:

  <input type="text" id="fname" name="fname">

   <script src="src/script.js"></script>

  </body>

</html>




Script.js

var firstName = document.getElementById("fname").value;

Output

TypeError: cannot read properties of null

Solution 3: Handle Property of Null Values

When we try to access a property of a null object, we face a type error that can crash our web application. Here we have the following ways to handle null values:

  1. Use the if structure
  2. Use the ternary operator
  3. Use the try-catch block

We have four ways to handle null values; now, let’s see these four ways one by one.

We can check whether the value is null with the help of most simple way, that is, if else statement. Now let’s see a piece of code to check null values:

Code

console.log("Handle null with if else statement");

let myvariable=null;

if (myvariable) 

{

  console.log("The value of variable is:" ,myvariable.value);

} else 

{

  console.log('Your variable contains null');

}

Output

Handle null with if else statement

Your variable contains null

We can use the ternary operator to handle a null value; it is a little more complicated than if statement. Now let’s understand it with the help of an example:

Code

console.log("Handle null with the ternary operator);

let myvariable=null;

const myval = myvariable? myvariable.value : 'default';

console.log("The value of the variable is:" , myval);

Output

Handle null with the ternary operator

The value of the variable is: default

Lastly, we can save our web application from crashing by simply putting a try-and-catch block. Now let’s see an example in which we use try catch to handle a null value:

Code

console.log("Handle null with ternary operator");

let myvariable=null;

try

{

    let myval = myvariable.value;

}

catch(err){

  console.log(err.message);

}

Output

Handle null with ternary operator

Cannot read property 'value' of null

Solution 4: Check if The Object Is Null or Undefined

Make sure that the object you are trying to access is not null or undefined. If it is, you will get this error.

Solution 5: Check for Typo Errors

Make sure you have typed the object and property names correctly. A common mistake is spelling the object or property name incorrectly.

Solution 6: Check if the object and property exist

Make sure that the object and property you are trying to access actually exist. If you are trying to access an object or property that does not exist, you will get this error.

Solution 7: Use Type Checking

You can use type checking to ensure that the object is not null or undefined before trying to access its properties. For example, you can use the “typeof” operator to check the type of the object, like this:

if (typeof object !== "undefined" && object !== null) {
    // access object properties
}

Conclusion

In conclusion, TypeError: cannot read properties of null is a common error that occurs in JavaScript when you try to access a value of null or commit a spelling mistake.

This article shows how to fix JavaScript’s “TypeError: cannot read properties of null” error. We have discussed all the reasons and their solutions, so now you can eliminate erroneous lines in your code.

Let’s have a quick recap of the topics discussed above.

  1. What is a Null?
  2. What is DOM?
  3. Causes of TypeError: cannot read properties of null in JavaScript.
  4. How can we fix TypeError: cannot read properties of null in JavaScript?

Finally, you significantly understand the “TypeError: cannot read properties of null” error in JavaScript; it’s time to remember the concepts; comment below 👇 the most straightforward way of handling null value.

Источник

When running JavaScript code, you might encounter an error that says:

Uncaught TypeError: Cannot read properties of null (reading 'x')

This error occurs when you try to read a property of an object, but the object itself is actually null so the property doesn’t exist.

Let me show you an example that causes this error and how I fix it.

How to reproduce this error

Suppose you write some JavaScript code to select an element from the DOM and read its value using the .value property.

You might write code as follows:

let inputEl = document.getElementById("text-input");

let inputVal = inputEl.value;

The code above tries to fetch an element that has an id of text-input. When the element isn’t found, then JavaScript will return null.

In the second line, we tried to read the value property of the inputEl object. If the inputEl object is null, then the error occurs:

Uncaught TypeError: Cannot read properties of null (reading 'value')

Variations of this error might occur depending on what property you’re trying to access.

For example, you can also try to call the addEventListener() method on a button object as follows:

let btnEl = document.getElementById("my-button");

console.log(btnEl); // null

btnEl.addEventListener("click", () => alert("You clicked a button!"));

When the getElementById() method can’t find the button, it returns null, so calling the addEventListener() method generates the error:

Uncaught TypeError: Cannot read properties of null (reading 'addEventListener')

As you can see, calling a property from an element that doesn’t exist will cause this error.

How to fix this error

To resolve this error, you need to make sure that you’re not accessing properties of a null object.

You can do so by adding an if statement before accessing the property. For example:

let inputEl = document.getElementById("text-input");

if (inputEl) {
  let inputVal = inputEl.value;
}

The if statement above will check if the variable inputEl is not null before running the code block.

This way, the value property from the inputEl object won’t be called when the inputEl is null.

The same goes for the button element. As an alternative, you can also use the optional chaining operator ?. as follows:

let btnEl = document.getElementById("my-button");

btnEl?.addEventListener("click", () => alert("You clicked a button!"));

This way, the addEventListener() method is only called when the btnEl variable isn’t null.

Sometimes, you also get this error even when the element exists on your page. If this is the case, then you need to make sure that you run the JavaScript code after the page content has been loaded.

Make sure that you place your <script> tag before the closing </body> tag as shown below:

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Nathan Sebhastian</title>
  </head>
  <body>
    <button id="btn">Sign up</button>
    <!-- ✅ Script is placed before the closing body tag -->
    <script>
      let btnEl = document.getElementById("my-button");

      btnEl?.addEventListener("click", () => alert("You clicked a button!"));
    </script>
  </body>
</html>

It doesn’t matter whether you have an inline or external script. You need to place it after the HTML elements.

Another way to ensure the script is executed after the content has been loaded is to listen for the DOMContentLoaded event from the document object as shown below:

document.addEventListener('DOMContentLoaded', () => {
  let btnEl = document.getElementById("my-button");

  btnEl?.addEventListener("click", () => alert("You clicked a button!"));
});

By wrapping your JavaScript code inside the addEventListener() method for the DOMContentLoaded event, you make sure that the code only gets executed after the content is loaded.

And that’s how you fix the TypeError: Cannot read properties of null when running JavaScript code.

I hope this tutorial helps. See you in other tutorials! 👋

Источник

Having a hard time fixing “Uncaught typeerror cannot read property of null” in your Javascript Code?

Worry no more! Because this article is for you.

In this article, we will discuss what this Typeerror means, the possible causes of why this error occurs, and provide solutions to resolve this error.

First, let us know what “uncaught typeerror: cannot read properties of null” means.

The “uncaught typeerror: cannot read properties of null” is an error message that occurs in Javascript.

It typically appears in the console of a web browser when a script attempts to access a property or method of a variable that is null or undefined.

In simpler terms, this error message means that a variable that is supposed to have a value is actually null or undefined.

As a result, the script cannot access the property or method that it needs.

So now let’s discover how his error occurs.

How does “Uncaught typeerror cannot read property of null” occurs?

The error message “Cannot read properties of null” typically occurs due to two main reasons:

  • Trying to access the value property of a null or undefined value.

This can happen if you’re trying to manipulate or retrieve the value of a DOM element that doesn’t exist or hasn’t been loaded yet.

  • Placing your JavaScript code above the HTML code where the relevant DOM elements are declared.

This can cause the JavaScript to execute before the DOM elements are created or loaded.

It results in an error when trying to access the properties or values of those elements.

Here’s an example code snippet that can cause the “Cannot read properties of null” error:


  const el = null;
  console.log(el.value); 
// Try to access the value property of a null value

Output:

TypeError: Cannot read properties of null (reading 'value')

Now let’s fix this error.

“Uncaught typeerror cannot read property of null” – Solutions

Here are the alternative solutions to fix this “uncaught typeerror: cannot read properties of null” error:

Solution 1. Make sure that the element exists before attempting to access its value.

The “typeerror cannot read property of null” error is commonly caused by using the getElementById() method with an ID that doesn’t exist in the DOM.

For Example

const input = document.getElementById('does-not-exist');
  console.log(input); // null
  
  const value = input.value; // Try to access the value property of a null value

This will result in the method returning null instead of a reference to the actual element.

When trying to access the value property of a null value (in this case, a non-existent DOM element), the error occurs.

To solve this error, it’s important to make sure that the element with the provided ID actually exists in the DOM before attempting to access its value property.

Solution 2. Checking if the element exists before accessing its value property.

To prevent the error when trying to access the value property of a DOM element, One way is to use the optional chaining (?.) operator.

It allows you to safely access nested properties even if one of them is null or undefined.

Another method is to use the ternary operator to conditionally assign a value based on whether an element exists or not.

You can also use a simple if statement to check if an element exists before accessing its value property.

Here’s an Example:

  const container = document.getElementById('container');
  const button = container.querySelector('.button');
  const message = container.querySelector('.message');

  // Using optional chaining ?.
  const buttonText1 = button?.innerText || '';

  // Using ternary operator
  const buttonText2 = button ? button.innerText : '';

  // Using if/else
  let buttonText3;
  if (button) {
    buttonText3 = button.innerText;
  } else {
    console.log('button is falsy');
    buttonText3 = '';
  }

  // Using nullish coalescing operator ??
  const messageText = message?.innerText ?? 'No message found';
  
  console.log(buttonText1);
  console.log(buttonText2);
  console.log(buttonText3);
  console.log(messageText);

Solution 3. Place the JS script tag at the bottom of the body tag.

It’s recommended to place the JS script tag at the bottom of the body tag in your HTML file.

This ensures that the HTML elements are loaded before the JS code is executed, which prevents the error from occurring.

By placing the script tag at the bottom, you also ensure that the page content is loaded first

Also, it can improve the perceived performance of your web page.

For Example:

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
  </head>
  <body>
    <input
      id="first_name"
      type="text"
      name="first_name"
      value="Initial Value"
    />

    <!-- script is run after input is declared -->
    <script>
    const input = document.getElementById('first_name');
    console.log(input); //  input#first_name

      //Works
      const value = input.value;
      console.log(value); // "Initial value"
    </script>
  </body>
</html>

I hope one or more of the given solutions above will help you solve your problem regarding “Uncaught typeerror cannot read property of null”.

Here are the other fixed Python errors that you can visit, you might encounter them in the future.

  • Attributeerror module tensorflow compat v1 has no attribute contrib
  • Attributeerror: module ‘collections’ has no attribute ‘iterable’ 
  • Attributeerror module has no attribute

Conclusion

In conclusion, In this article, we discuss the “Uncaught typeerror cannot read property of null”, provide the possible causes, give solutions, and resolve the error.

By following the given solution, surely you can fix the error quickly and proceed to your coding project again.

I hope this article helps you to solve your problem regarding this TypeError.

We’re happy to help you.

Happy coding! Have a Good day and God bless.

Источник

The error “Cannot read properties of null reading useState usage” usually occurs when you are trying to access the properties of a null object. In the case of React and TypeScript, it can happen when you are trying to access the state of a component before it has been initialized. To fix this error, you need to make sure that you are initializing your state properly before trying to access it. Here are a few things you can check. Make sure you have properly initialized your state with the useState hook. For example:

const [myState, setMyState] = useState(null);

Check that you are not trying to access the state before it has been set. You can use conditional rendering to make sure the component doesn’t render until the state has been initialized

if (!myState) {
  return null;
}

If you are passing state as a prop to a child component, make sure you are passing a non-null value. You can use optional chaining to handle null values

// Parent component
<MyChildComponent myProp={myState?.myValue} />

// Child component
interface MyChildProps {
  myProp?: string;
}

function MyChildComponent({ myProp }: MyChildProps) {
  // Check that myProp is not null before using it
  if (!myProp) {
    return null;
  }

  // Render component using myProp
}

You should be able to fix the Cannot read properties of null reading useState error in your React TypeScript application

Solution to useState

You need to use and define the state / useState inside the main function.

Источник

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