Types of Errors in JavaScript
When working with JavaScript, you will encounter three main types of errors: syntax errors, runtime errors, and logical errors. Understanding these categories is essential for identifying problems in your code and applying the right solutions.
A syntax error occurs when the rules of the JavaScript language are broken. The JavaScript engine cannot parse or execute code with syntax errors, so these are typically caught before the code even runs. Missing parentheses, incorrect punctuation, or misspelled keywords are common causes.
A runtime error happens while the program is running. These errors occur when the code is syntactically correct, but something goes wrong during execution—such as trying to access a property of an undefined object, or calling a function that does not exist.
123456// Syntax error example: missing closing parenthesis console.log("Hello, world!"; // Runtime error example: trying to access a property of undefined let user; console.log(user.name);
Logical errors are different from syntax and runtime errors. The code runs without producing error messages, but the output is not what you intended. These errors are often the hardest to detect because the JavaScript engine does not report them.
For instance, if you accidentally use the wrong operator or misplace a condition, your program may run but behave incorrectly. In the code sample above, both the syntax and runtime errors will stop your code or throw visible exceptions.
However, if you wrote a function to add two numbers but accidentally subtracted them instead, you would have a logical error. The code would execute, but the results would be wrong.
Recognizing the distinction between these error types helps you choose the right debugging approach and prevents you from overlooking subtle mistakes in your logic.
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When working with JavaScript, you will encounter three main types of errors: syntax errors, runtime errors, and logical errors. Understanding these categories is essential for identifying problems in your code and applying the right solutions.
A syntax error occurs when the rules of the JavaScript language are broken. The JavaScript engine cannot parse or execute code with syntax errors, so these are typically caught before the code even runs. Missing parentheses, incorrect punctuation, or misspelled keywords are common causes.
A runtime error happens while the program is running. These errors occur when the code is syntactically correct, but something goes wrong during execution—such as trying to access a property of an undefined object, or calling a function that does not exist.
123456// Syntax error example: missing closing parenthesis console.log("Hello, world!"; // Runtime error example: trying to access a property of undefined let user; console.log(user.name);
Logical errors are different from syntax and runtime errors. The code runs without producing error messages, but the output is not what you intended. These errors are often the hardest to detect because the JavaScript engine does not report them.
For instance, if you accidentally use the wrong operator or misplace a condition, your program may run but behave incorrectly. In the code sample above, both the syntax and runtime errors will stop your code or throw visible exceptions.
However, if you wrote a function to add two numbers but accidentally subtracted them instead, you would have a logical error. The code would execute, but the results would be wrong.
Recognizing the distinction between these error types helps you choose the right debugging approach and prevents you from overlooking subtle mistakes in your logic.
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