# Error Handling in JavaScript: Try, Catch, Finally

## Introduction

Let's suppose you have made an A.T.M transcation from a ABC atm machine You have entered the the amount and password of the debit card then just suddenly the atm machine frezzes and didn't responding anything on any key pressing Just imagine the frustration level of the Customer  
That's why the error handling comes in the picture

Error handling is the one of great feature of javascript

## What errors are in JavaScript ?

In any language errors happens when you can not execute a piece of code then the language returns a failure

In JavaScript when you try to execute somthing that JavaScript can not understand it throws an error, Which stops your application

## Common types of errors

Here are some few very common errors found in JavaScript

### Reference Error

This error comes when you try to used some value of variable that never be declared

**Example:**

```javascript
console.log(fname);
//It gave error because fname is not defined
```

### Type Error

This error comes when the type is not same as the expected, When you are trying to perform a operation on something that does not supports

**Example :**

```javascript
(234).toUpperCase()
```

### Syntax Error

This error comes when you typed the wrong syntax of some code , or you have destructured the code because of that the interpreter can not understand the structure of your code

**Example :**

```javascript
function abc({
    //code
}
```

### Range Error

This error comes when your typed value is out of range

**Example :**

```javascript
new Array(-1);
```

## Error Handling

Error handling means that you are handling the error so that your application doesn't crash or freeze when an error occured.

### Using `try` and `catch` blocks

The common error handling method is using try catch tool to handle the errors

`try` : in this block you write that code that might be failed

`catch`: in this block you handles that if error comes in try block you will handle it in catch block

**Example :**

```javascript
try {
  let data = JSON.parse(invalidJsonString); // This might fail!
  console.log(data);
} catch (error) {
  console.error("We couldn't read the data:", error.message);
}
```

### The `finally` block

In this block we write the code that will be run whether the error comes or not this block will always run

**Example :**

```javascript
try {
  let data = JSON.parse(invalidJsonString); // This might fail!
  console.log(data);
} catch (error) {
  console.error("We couldn't read the data:", error.message);
}finally {
  console.log("Ended")
}
```

## Throwing custom errors

Sometimes the code is working and there will no error occured but we didn't want to allow the user to cross the limit or don't want to access him

### Example :

```javascript
function withdraw(amount) {
  if (amount > 5000) {
    throw new Error("Daily limit exceeded");
  }
  return "Withdrawal successful";
}

try {
  console.log(withdraw(7000));
} catch (err) {
  console.log(err.message);
}
```

## Conclusion :

The try , catch , finally are the very good features of JavaScript to handle the errors gracfully, we don't want to crash or freeze our application so we use these to handle the unexpected failures...