docs(10_Wiki): W3Schools 위키화 — HTML/CSS/JavaScript(core)
W3Schools 튜토리얼을 P-Reinforce v3.1 포맷으로 위키화(영어 본문, 한/영 섹션 헤더). - Topic_HTML: 59문서 (튜토리얼+예제, 레퍼런스/메타 제외) - Topic_CSS: 190문서 (메인 + Advanced/Flexbox/Grid/RWD 전체) - Topic_JavaScript: 120문서 (코어 언어; Temporal/DOM상세/BOM/WebAPI/AJAX/jQuery/Graphics 등은 후속) 각 폴더 00_INDEX.md(MOC) 포함. 코드 verbatim, 미확인분은 "Not found in source" 표기. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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---
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id: javascript-number-methods
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title: "JavaScript Number Methods"
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category: "Frontend"
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status: "draft"
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verification_status: "conceptual"
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canonical_id: ""
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aliases: ["number methods", "toFixed", "toPrecision", "Number()", "parseInt", "parseFloat"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.89
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created_at: 2026-06-23
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updated_at: 2026-06-23
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review_reason: ""
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merge_history: []
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tags: ["javascript", "js", "web", "frontend", "w3schools", "numbers", "number-methods", "parsing"]
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raw_sources: ["https://www.w3schools.com/js/js_number_methods.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[JavaScript Number Methods]]
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## 🎯 한 줄 통찰 (One-line insight)
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Basic number methods (`toString`, `toExponential`, `toFixed`, `toPrecision`, `valueOf`) work on any number, while static `Number.*` methods (`isInteger`, `isFinite`, `isNaN`, `isSafeInteger`, `parseInt`, `parseFloat`) can only be used on `Number` itself. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **Basic methods work on any number** — `toString()`, `toExponential()`, `toFixed()`, `toPrecision()`, `valueOf()`. [S1]
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- **Static methods only on `Number`** — `Number.isFinite()`, `Number.isInteger()`, `Number.isNaN()`, `Number.isSafeInteger()`, `Number.parseInt()`, `Number.parseFloat()`. [S1]
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- **`toString()`** — returns a number as a string; accepts a radix. [S1]
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- **`toFixed()`** — returns a string with a specified number of decimals; perfect for working with money. [S1]
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- **`toPrecision()`** — returns a string with a number written to a specified length. [S1]
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- **Conversion functions** — `Number()`, `parseInt()`, `parseFloat()` convert variables to numbers; `NaN` is returned when conversion fails. [S1]
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- **Methods cannot be used on variables for statics** — `Number.isInteger()` etc. must be called on `Number`; calling on a variable throws a TypeError. [S1]
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- **Safe integers** — range is -(2⁵³ - 1) to +(2⁵³ - 1); `9007199254740991` is safe, `9007199254740992` is not. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **Format money** — `value.toFixed(2)` to render two decimal places. [S1]
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- **Parse leading number from text** — `parseInt("10 years")` / `parseFloat("10.33")` extract a number from the front of a string. [S1]
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- **Validate before use** — `Number.isInteger()` / `Number.isSafeInteger()` / `Number.isNaN()` to check values. [S1]
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## 📖 세부 내용 (Details)
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**Basic Methods** can be used on any number: `toString()`, `toExponential()`, `toFixed()`, `toPrecision()`, `valueOf()`. **Static Methods** can only be used on `Number`: `Number.isFinite()`, `Number.isInteger()`, `Number.isNaN()`, `Number.isSafeInteger()`, `Number.parseInt()`, `Number.parseFloat()`. [S1]
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**toString()** — returns a number as a string; can take a radix. [S1]
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```javascript
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let x = 123;
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x.toString();
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(123).toString();
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(100 + 23).toString();
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```
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```javascript
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let x = 123;
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let text = x.toString(2);
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```
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**toExponential()** — returns a string with a number rounded and written using exponential notation. [S1]
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```javascript
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let x = 9.656;
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x.toExponential(2);
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x.toExponential(4);
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x.toExponential(6);
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```
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**toFixed()** — returns a string with the number written with a specified number of decimals; perfect for working with money. [S1]
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```javascript
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let x = 9.656;
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x.toFixed(0);
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x.toFixed(2);
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x.toFixed(4);
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x.toFixed(6);
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```
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**toPrecision()** — returns a string with a number written with a specified length. [S1]
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```javascript
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let x = 9.656;
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x.toPrecision();
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x.toPrecision(2);
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x.toPrecision(4);
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x.toPrecision(6);
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```
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**valueOf()** — returns a number as a number; used internally in JavaScript to convert Number objects to primitive values. [S1]
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```javascript
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let x = 123;
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x.valueOf();
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(123).valueOf();
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(100 + 23).valueOf();
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```
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**Converting Variables to Numbers** — three methods are available: [S1]
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| Method | Description |
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|--------|-------------|
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| Number() | Converts argument to number |
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| parseFloat() | Parses argument, returns floating point |
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| parseInt() | Parses argument, returns whole number |
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**Number()** — converts its argument to a number. [S1]
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```javascript
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Number(true);
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Number(false);
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Number("10");
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Number(" 10");
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Number("10 ");
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Number(" 10 ");
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Number("10.33");
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Number("10,33");
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Number("10 33");
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Number("John");
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```
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**Number() Used on Dates** — converts a date to milliseconds. [S1]
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```javascript
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Number(new Date("1970-01-01"))
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```
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```javascript
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Number(new Date("1970-01-02"))
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```
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```javascript
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Number(new Date("2017-09-30"))
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```
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**parseInt()** — parses and returns a whole number. [S1]
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```javascript
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parseInt("-10");
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parseInt("-10.33");
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parseInt("10");
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parseInt("10.33");
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parseInt("10 20 30");
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parseInt("10 years");
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parseInt("years 10");
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```
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**parseFloat()** — parses and returns a floating point number. [S1]
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```javascript
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parseFloat("10");
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parseFloat("10.33");
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parseFloat("10 20 30");
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parseFloat("10 years");
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parseFloat("years 10");
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```
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**Number Object Methods** (static): [S1]
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| Method | Description |
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|--------|-------------|
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| Number.isInteger() | Returns true if argument is integer |
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| Number.isNaN() | Returns true if argument is NaN |
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| Number.isFinite() | Returns true if not Infinity or NaN |
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| Number.isSafeInteger() | Returns true if safe integer |
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| Number.parseFloat() | Converts string to number |
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| Number.parseInt() | Converts string to whole number |
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Number methods can only be accessed like `Number.isInteger()`; calling them on a variable produces a TypeError ("X.isInteger is not a function"). `Number.isNaN()` is the preferred way to check for equality with NaN. [S1]
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**Number.isInteger()** [S1]
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```javascript
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Number.isInteger(10);
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Number.isInteger(10.5);
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```
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**Number.isFinite()** [S1]
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```javascript
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Number.isFinite(123);
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```
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**Number.isNaN()** [S1]
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```javascript
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Number.isNaN(123);
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```
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**Number.isSafeInteger()** — safe integer range is -(2⁵³ - 1) to +(2⁵³ - 1). [S1]
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```javascript
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Number.isSafeInteger(10);
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Number.isSafeInteger(12345678901234567890);
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```
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**Number.parseFloat()** [S1]
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```javascript
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Number.parseFloat("10");
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Number.parseFloat("10.33");
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Number.parseFloat("10 20 30");
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Number.parseFloat("10 years");
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Number.parseFloat("years 10");
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```
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**Number.parseInt()** [S1]
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```javascript
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Number.parseInt("-10");
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Number.parseInt("-10.33");
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Number.parseInt("10");
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Number.parseInt("10.33");
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Number.parseInt("10 20 30");
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Number.parseInt("10 years");
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Number.parseInt("years 10");
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```
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## 🛠️ 적용 사례 (Applied in summary)
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The page's own snippets are the canonical applied examples — formatting `9.656` with `toFixed`/`toPrecision`/`toExponential`, converting strings and dates with `Number()`, parsing with `parseInt`/`parseFloat`, and validating with the static `Number.*` methods. No external project/commit applications found in the source.
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## 💻 코드 패턴 (Code patterns)
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Format for money:
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```javascript
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let x = 9.656;
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x.toFixed(2);
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```
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Parse a number from text:
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```javascript
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parseInt("10 years");
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parseFloat("10.33");
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```
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Validate a value:
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```javascript
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Number.isInteger(10);
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Number.isSafeInteger(9007199254740991);
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```
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## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)
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- **`Number()` vs `parseInt()` vs `parseFloat()`** — `Number()` converts the whole argument (returns NaN if it is not fully numeric, e.g. `"10 33"`); `parseInt()` returns a whole number from the leading numeric portion; `parseFloat()` returns a floating point from the leading numeric portion. [S1]
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- **Basic vs static methods** — basic methods (`toFixed`, etc.) are called on a number value; static methods (`Number.isInteger`, etc.) must be called on `Number` itself or they throw a TypeError. [S1]
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- **`Number.isNaN()` is preferred** for checking equality with NaN. [S1]
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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No contradictions found in the source.
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## ✅ 검증 상태 및 신뢰도
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- **상태:** draft
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- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
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- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
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- **신뢰 점수:** 0.89
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- **중복 검사 결과:** 신규 생성 (New discovery)
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## 🔗 지식 그래프 (Knowledge Graph)
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- **상위/루트:** [[JavaScript Tutorial]]
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- **관련 개념:** [[JavaScript Numbers]], [[JavaScript Number Properties]], [[JavaScript Data Types]], [[JavaScript Operators]]
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- **참조 맥락:** Referenced whenever formatting numbers for display or converting strings/dates into numeric values.
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## 📚 출처 (Sources)
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- [S1] W3Schools — JavaScript Number Methods — https://www.w3schools.com/js/js_number_methods.asp
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## 📝 변경 이력 (Change history)
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- 2026-06-23: Initial draft synthesized from the W3Schools "JavaScript Number Methods" page (Astra wiki-curation, P-Reinforce v3.1 format).
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