JavaScriptは少数が苦手

2022/2/22 はじめてのIT勉強会（仙台）

Transcript

1. JavaScript͸খ਺͕ۤख ʙුಈখ਺఺ܭࢉ͸ਖ਼֬ʹͰ͖ͳ͍ʙ 2022/2/22ɹגࣜձࣾBTMɹੴࠇ
2. 0.3 - 0.1 = ?
3. console.log( 0.3 - 0.1 ) > 0.19999999999999998
4. ·͔͡ɺJavaScript... σΩΔࢠͩͱࢥ͍ͬͯͨͷʹ...
5. JavaScriptͰখ਺Λ࢖ͬͨܭࢉ͸ཁ஫ҙ • ޡࠩͷݪҼɹ ɹ 10ਐ਺ͷখ਺͸ 2ਐ਺ʹ͏·͘ม׵͕Ͱ͖ͳ͍ͱ͖͕͋Δ͔Β ɹ(͖ͬ͞ͷྫ)ɹ0.2 Λ2ਐ਺ม׵ɹ὎ɹ0.00110011.....ʢ॥؀খ਺ʣ • JavaScriptͷ਺஋͸Numberܕ ɹුಈখ਺఺਺ʢIEEE754ʣΛ࠾༻
6. ࣮ࡍʹ͋ͬͨࠔͬͨ࿩ ͱ͋Δ͓٬༷ͷCRMʢސ٬؅ཧγεςϜʣͰ ߹ܭֹۚʢ੫ࠐʣͷֹ͕ۚ߹Θͳ͍
7. ͲΜͳܭࢉʁ ߹ܭֹۚʢ੫ࠐʣ͕߹Θͳ͍ ߹ܭֹۚ(੫ൈ) ফඅ੫ֹ(10%) ߹ܭֹۚ(੫ࠐ) : 3,000,000ԁ : 300,000ԁ : 3,300,000ԁ Α͋͘Δ՝੫ܭࢉͰ͢
8. ͲΜͳ෩ʹ߹Θͳ͔ͬͨͷʁ ߹ܭֹۚʢ੫ࠐʣ͕߹Θͳ͍ Math.ceil(3000000 * 1.1) > 3300001 ߹ܭֹۚ(੫ൈ) ফඅ੫ֹ(10%) ߹ܭֹۚ(੫ࠐ) : 3,000,000ԁ : 300,000ԁ : 3,300,000ԁ
9. ͲΜͳ෩ʹ߹Θͳ͔ͬͨͷʁ ߹ܭֹۚʢ੫ࠐʣ͕߹Θͳ͍ Math.ceil(3000000 * 1.1) > 3300001 ߹ܭֹۚ(੫ൈ) ফඅ੫ֹ(10%) ߹ܭֹۚ(੫ࠐ) : 3,000,000ԁ : 300,000ԁ : 3,300,000ԁ ̍ԁͣΕͨɾɾɾ 3,300,001ԁ
10. ͳͥ߹Θͳ͔ͬͨͷʁ ߹ܭֹۚʢ੫ࠐʣ͕߹Θͳ͍ Math.ceil (3000000 * 1.1) > 3300001 // NG A . গ਺ͷޡࠩʴؙΊॲཧͷ͍ͤͰ͢ খ਺Λ੾Γ্͛ͯ੔਺ʹ͢Δ 3300000.0000000005
11. Ͳ͏͢Ε͹ྑ͔ͬͨʁ ߹ܭֹۚʢ੫ࠐʣ͕߹Θͳ͍ Math.ceil (3000000 * 110 / 100) > 3300000 // OK A . ʢҊͦͷ̍ʣܭࢉʹখ਺Λ࢖Θͳ͍ 3300000
12. Ͳ͏͢Ε͹ྑ͔ͬͨʁ ߹ܭֹۚʢ੫ࠐʣ͕߹Θͳ͍ Math.ceil(BigNumber(3000000).times(1.1)) > 3300000 // OK A . ʢҊͦͷ̎ʣখ਺ܭࢉ༻ϥΠϒϥϦΛ࢖༻͢Δ 3300000 bignumber.jsΛ࢖ͬͨྫ
13. ුಈখ਺఺(float΍double)Ͱ͸ͳ͍ܕ΍ΫϥεΛ࢖͓͏ ଞͷݴޠ͸ʁ Java Ruby MySQL BigDecimal BigDecimal DECIMAL, NUMERIC
14. খ਺ΛؚΉܭࢉ͸ਖ਼֬ͳ݁Ռ͕ग़ͳ͍͜ͱ͕͋Δ ·ͱΊ ͳΔ΂͘੔਺ʹஔ͖׵͑ͯܭࢉ͢Δ ුಈখ਺఺Ͱ͸ͳ͘ݻఆখ਺఺ͷܕ΍ΫϥεΛ࢖͏ ͍͟ͱͳͬͨΒখ਺ܭࢉ༻ͷϥΠϒϥϦͳͲ࢖༻Λݕ౼ 0.3 - 0.1 number, float, double ( 3 - 1 ) / 10 decimalܥ JavaScriptͳΒbignumber.js΍decimal.js
15. ͜ΕͰ΋͏ɺখ਺ܭࢉ͸ා͘ͳ͍Ͱ͢Ͷʂ ऴΘΔલʹͪΐͬͱ͚ͩએ఻...
16. ͝ਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠