2nd/10_Wiki/Topic_JavaScript/JavaScript_Errors_Intro.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-errors-intro	JavaScript Errors Intro	Frontend	draft	conceptual		JavaScript errors try catch throw ReferenceError TypeError RangeError error handling		B	0.88	2026-06-23	2026-06-23			javascript js web frontend w3schools errors try-catch	https://www.w3schools.com/js/js_errors_intro.asp

JavaScript Errors Intro

🎯 한 줄 통찰 (One-line insight)

Errors will happen in running JavaScript code; try tests a block for runtime errors and catch handles them via an error object whose name identifies the error type. [S1]

🧠 핵심 개념 (Core concepts)

• Errors will happen — many error types can occur during execution: Reference Errors, Type Errors, Range Errors, URI Errors, Syntax Errors, and Eval Errors. [S1]
• try / catch — the try statement tests a block of code for errors during execution; the catch statement handles the error if one occurs. [S1]
• The error object — the catch block receives an error object; err.name returns the type of error. [S1]
• Syntax errors are special — a SyntaxError happens before runtime, so it is not catchable by ordinary try...catch. [S1]
• EvalError is legacy — newer JavaScript versions raise SyntaxError instead of EvalError. [S1]

🧩 추출된 패턴 (Extracted patterns)

• Wrap risky code, inspect err.name — put the operation that may fail inside try, then read err.name in catch to discover which error type occurred. [S1]
• Trigger by error category — each error type is provoked by a distinct kind of mistake: undefined references → ReferenceError; wrong-type operations → TypeError; out-of-range values → RangeError; illegal URI characters → URIError. [S1]

📖 세부 내용 (Details)

Errors Will Happen! While executing JavaScript code, different errors can occur, including Reference Errors, Type Errors, Range Errors, URI Errors, Syntax Errors, and Eval Errors. [S1]

How to Handle JavaScript Errors The try statement tests a block of code for errors during execution, while catch handles errors if they occur. [S1]

Reference Errors A ReferenceError occurs when referencing a variable that doesn't exist or accessing a variable before initialization. [S1]

Using a non-existing variable: [S1]

let x = 5;

try {
  x = y + 1;
} catch(err) {
  let text = err.name;
}

Accessing a variable before initialization: [S1]

try {
  let x = y;
  let y = 5;
} catch(err) {
  let text = err.name;
}

JavaScript Type Errors A TypeError occurs when a value is the wrong type or an operation is invalid on that type. [S1]

Calling a non-function: [S1]

let anna = 5;
try {
  anna(5);
} catch(err) {
  let text = err.name;
}

Invalid method on a number: [S1]

let num = 1;
try {
  num.toUpperCase();
} catch(err) {
  let text = err.name;
}

JavaScript Range Errors A RangeError occurs when a value falls outside its valid range. [S1]

Invalid array length: [S1]

try {
  new Array(-1);
} catch(err) {
  let text = err.name;
}

Invalid precision argument: [S1]

let num = 1;

try {
  num.toPrecision(500);
} catch(err) {
  let text = err.name;
}

JavaScript URI Errors A URIError occurs with illegal characters in URI functions. [S1]

try {
  decodeURI("%%%");
} catch(err) {
  document.getElementById("demo").innerHTML = err.name;
}

JavaScript Syntax Errors A SyntaxError occurs when code violates JavaScript grammar rules. Syntax errors are not catchable by try...catch because they happen before runtime. [S1]

try {
  let x = Math.round(4.6;)
} catch(err) {
  let text = err.name + " " + err.description;
}

JavaScript Eval Error An EvalError indicates an error in the eval() function. Newer JavaScript versions use SyntaxError instead. [S1]

🛠️ 적용 사례 (Applied in summary)

The page's own snippets are the canonical applied examples — each wraps a deliberate mistake in try and reads err.name in catch to surface the resulting error type. No external project/commit applications found in the source.

💻 코드 패턴 (Code patterns)

Wrap risky code and inspect the error type (language: JavaScript):

try {
  // code that may throw
} catch(err) {
  let text = err.name;
}

Provoke each error category:

x = y + 1;        // ReferenceError (y not defined)
anna(5);          // TypeError (anna is not a function)
new Array(-1);    // RangeError (invalid array length)
decodeURI("%%%"); // URIError (illegal URI characters)

⚖️ 모순 및 업데이트 (Contradictions & updates)

• EvalError deprecation — the source notes that newer JavaScript versions raise SyntaxError instead of EvalError, so EvalError is effectively legacy. [S1]

✅ 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 Silent Errors, JavaScript Error Statements, JavaScript Error Object, JavaScript Debugging
• 참조 맥락: The starting point for understanding which JavaScript error types exist and how try...catch surfaces them.

📚 출처 (Sources)

• [S1] W3Schools — JavaScript Errors Intro — https://www.w3schools.com/js/js_errors_intro.asp

📝 변경 이력 (Change history)

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