2nd/10_Wiki/Topic_JavaScript/JavaScript_Errors.md

id, title, category, status, verification_status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, created_at, updated_at, review_reason, merge_history, tags, raw_sources, applied_in, github_commit

id	title	category	status	verification_status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	created_at	updated_at	review_reason	merge_history	tags	raw_sources	applied_in	github_commit
javascript-error-statements	JavaScript Error Statements	Frontend	draft	conceptual		try catch finally throw statement error statements input validation exception handling		B	0.88	2026-06-23	2026-06-23			javascript js web frontend w3schools errors try-catch throw	https://www.w3schools.com/js/js_errors.asp

JavaScript Error Statements

🎯 한 줄 통찰 (One-line insight)

The try, catch, finally, and throw statements form JavaScript's error-handling block: try risky code, catch failures, optionally always run cleanup in finally, and raise custom errors with throw. [S1]

🧠 핵심 개념 (Core concepts)

• The try statement handles errors during execution without stopping the program; it works with catch, and optionally finally and throw. [S1]
• The try block holds code that might throw an error; the catch block is skipped if no error occurs. [S1]
• The catch block executes only if an error occurs in the try block, providing error details through an error object. [S1]
• The finally block (optional) runs after try and catch regardless of outcome, typically for cleanup. [S1]
• JavaScript throws errors by creating an Error object with name and message properties. [S1]
• The throw statement lets you create custom errors; you can throw strings, numbers, booleans, or objects. [S1]

🧩 추출된 패턴 (Extracted patterns)

• Validate-then-throw — check input conditions and throw a descriptive value for each failure, then format a message in catch. [S1]
• Always clean up in finally — use finally to reset state (e.g. clear an input field) whether or not an error occurred. [S1]
• JS + HTML validation combo — modern browsers often combine JavaScript with built-in HTML validation rules defined in HTML attributes (e.g. min, max, step). [S1]

📖 세부 내용 (Details)

The Try Statement The try statement handles errors during code execution without stopping the program. It works with catch, and optionally with finally and throw. [S1]

The Try Block / The Catch Block The try block contains code that might throw an error; the catch block is skipped if no error occurs. The catch block executes only if an error occurs, providing error details through an error object: [S1]

try {
  // Code that may cause an error
} catch (error) {
  // Code to handle the error
}

The Finally Block (Optional) The finally block executes after try and catch regardless of outcome, typically for cleanup tasks: [S1]

try {
  // Block of code to try
} catch(err) {
  // Block of code to handle errors
} finally {
  // Block of code to be executed regardless of the try / catch result
}

JavaScript Throws Errors When errors occur, JavaScript creates an Error object with name and message properties. [S1]

The Throw Statement The throw statement allows creation of custom errors and can throw strings, numbers, booleans, or objects. [S1]

Input Validation Example Validates a number between 5 and 10, throwing "empty", "not a number", "too low", or "too high" as appropriate: [S1]

function myFunction() {
  const message = document.getElementById("p01");
  message.innerHTML = "";
  let x = document.getElementById("demo").value;
  try {
    if(x.trim() == "") throw "empty";
    if(isNaN(x)) throw "not a number";
    x = Number(x);
    if(x < 5) throw "too low";
    if(x > 10) throw "too high";
  } catch(err) {
    message.innerHTML = "Input is " + err;
  }
}

HTML Validation Modern browsers will often use a combination of JavaScript and built-in HTML validation, using predefined validation rules defined in HTML attributes. [S1]

Finally Example A function that validates input and uses finally to clear the input field regardless of validation outcome: [S1]

function myFunction() {
  const message = document.getElementById("p01");
  message.innerHTML = "";
  let x = document.getElementById("demo").value;
  try {
    if(x.trim() == "") throw "is empty";
    if(isNaN(x)) throw "is not a number";
    x = Number(x);
    if(x > 10) throw "is too high";
    if(x < 5) throw "is too low";
  } catch(err) {
    message.innerHTML = "Error: " + err + ".";
  } finally {
    document.getElementById("demo").value = "";
  }
}

🛠️ 적용 사례 (Applied in summary)

The two myFunction examples are the canonical applied cases — a numeric input validator that throws descriptive strings on bad input, and a variant that additionally clears the field in finally. No external project/commit applications found in the source.

💻 코드 패턴 (Code patterns)

Validate input by throwing descriptive values, then format in catch (language: JavaScript):

try {
  if(x.trim() == "") throw "empty";
  if(isNaN(x)) throw "not a number";
  x = Number(x);
  if(x < 5) throw "too low";
  if(x > 10) throw "too high";
} catch(err) {
  message.innerHTML = "Input is " + err;
}

Guarantee cleanup with finally:

try {
  // risky work
} catch(err) {
  // handle
} finally {
  document.getElementById("demo").value = "";
}

⚖️ 모순 및 업데이트 (Contradictions & updates)

No contradictions found in the source.

✅ 검증 상태 및 신뢰도

• 상태: draft
• 검증 단계: conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
• 출처 신뢰도: B (W3Schools — widely used educational reference, not a primary standards body)
• 신뢰 점수: 0.88
• 중복 검사 결과: 신규 생성 (New discovery)

🔗 지식 그래프 (Knowledge Graph)

• 상위/루트: JavaScript Tutorial
• 관련 개념: JavaScript Errors Intro, JavaScript Silent Errors, JavaScript Error Object, JavaScript Debugging
• 참조 맥락: The mechanics page for the four error keywords (try/catch/finally/throw) used to build robust input validation.

📚 출처 (Sources)

• [S1] W3Schools — JavaScript Error Statements — https://www.w3schools.com/js/js_errors.asp

📝 변경 이력 (Change history)

• 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Error Statements" page (Astra wiki-curation, P-Reinforce v3.1 format).