JavaScript : Errors

In JavaScript, errors occur when there is a mistake in the code or when something unexpected happens during the execution of the program. Errors can range from syntax errors that prevent the code from running to runtime errors that occur during execution. Here are some common types of errors in JavaScript:

1. Syntax Errors:

Syntax errors occur when the code violates the rules of the JavaScript syntax. These errors are detected by the JavaScript engine during the parsing phase, before the code is executed.

// Syntax Error: Missing closing parenthesis
if (condition {
    // Code block
}
 

2. Reference Errors:

Reference errors occur when trying to access a variable or function that is not defined or is out of scope.

// Reference Error: Variable is not defined
console.log(undefinedVariable);

function myFunction() {
    // Function scope
}

// Reference Error: Function is not defined
myFunction();
 

3. Type Errors:

Type errors occur when an operation is performed on a value of an inappropriate type.

// Type Error: Cannot read property 'length' of undefined
console.log(undefinedVariable.length);

// Type Error: Cannot assign to read only property 'x' of object
Object.freeze(obj);
obj.x = 10;
 

4. Range Errors:

Range errors occur when using an invalid index or parameter value, typically in methods that expect a certain range of values.

// Range Error: Invalid array length
const arr = new Array(-1);

// Range Error: Maximum call stack size exceeded
function recursiveFunction() {
    recursiveFunction();
}
recursiveFunction();
 

5. Eval Errors:

Eval errors occur when there is an issue with the eval() function, such as incorrect syntax in the evaluated code.

// Eval Error: Octal literals are not allowed in strict mode
eval('010');
 

6. Custom Errors:

Developers can also create custom errors using the Error constructor to handle specific situations in their code.

throw new Error('Custom error message');
 

Handling Errors:

To handle errors in JavaScript, you can use try...catch blocks to catch and handle exceptions gracefully.

try {
    // Code that might throw an error
} catch (error) {
    // Code to handle the error
    console.error(error.message);
}
 

Understanding and properly handling errors is essential for writing robust and reliable JavaScript code. It helps prevent unexpected crashes and improves the overall user experience of web applications.