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| const CALC_RE = /^[\d\s+\-*/().%]+$/ |
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| export function safeCalc(expression) { |
| if (typeof expression !== 'string' || !expression.trim()) { |
| return '計算錯誤：表達式為空' |
| } |
| if (!CALC_RE.test(expression)) { |
| return `計算錯誤：只支援數字與 + - * / ( ) . %（收到「${expression}」）` |
| } |
| try { |
| const value = evaluate(expression.replace(/\s+/g, '')) |
| if (!Number.isFinite(value)) return `計算錯誤：結果無效（${expression}）` |
| |
| return `計算結果：${Math.round(value * 1e10) / 1e10}` |
| } catch (e) { |
| return `計算錯誤：${expression}（${e.message}）` |
| } |
| } |
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| function evaluate(expr) { |
| let pos = 0 |
| const peek = () => expr[pos] |
| const take = () => expr[pos++] |
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| function parseExpr() { |
| let left = parseTerm() |
| while (peek() === '+' || peek() === '-') { |
| const op = take() |
| const right = parseTerm() |
| left = op === '+' ? left + right : left - right |
| } |
| return left |
| } |
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| function parseTerm() { |
| let left = parseFactor() |
| while (peek() === '*' || peek() === '/' || peek() === '%') { |
| const op = take() |
| const right = parseFactor() |
| left = op === '*' ? left * right : op === '/' ? left / right : left % right |
| } |
| return left |
| } |
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| function parseFactor() { |
| if (peek() === '-') { take(); return -parseFactor() } |
| if (peek() === '+') { take(); return parseFactor() } |
| if (peek() === '(') { |
| take() |
| const value = parseExpr() |
| if (peek() !== ')') throw new Error('括號不配對') |
| take() |
| return value |
| } |
| const start = pos |
| while (pos < expr.length && /[\d.]/.test(expr[pos])) pos++ |
| if (start === pos) throw new Error('預期數字') |
| const value = Number(expr.slice(start, pos)) |
| if (Number.isNaN(value)) throw new Error('數字格式錯誤') |
| return value |
| } |
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| const result = parseExpr() |
| if (pos !== expr.length) throw new Error('表達式有多餘字元') |
| return result |
| } |
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