Decoding JavaScript Errors

Errors in JavaScript are inevitable, but understanding them can make debugging easier. JavaScript has several built-in error types that can help you identify what went wrong in your code.


A ReferenceError is thrown when trying to dereference a variable that has not been declared.

console.log(nonExistentVariable) // Outputs: ReferenceError: nonExistentVariable is not defined


A TypeError is thrown when an operation could not be performed, typically when a value is not of the expected type.

null.f() // Outputs: TypeError: Cannot read property 'f' of null


A SyntaxError is thrown when trying to execute code with a syntactical error.

eval('hoo bar') // Outputs: SyntaxError: Unexpected identifier


A RangeError is thrown when a numeric variable or parameter is outside of its valid range.

new Array(-1) // Outputs: RangeError: Invalid array length

Understanding these error types can help you debug your JavaScript code more effectively.