2019-01-14 16:24:19 +09:00
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---
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title: padStartにおけるpadSizeの求め方
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2019-01-14 16:24:29 +09:00
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date: 2019-01-14 00:00:00 +09:00
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2019-08-14 21:24:49 +09:00
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redirect_from: "/blog/2019/01/14/padsize"
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2019-01-14 16:24:19 +09:00
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---
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2021-01-21 21:45:05 +09:00
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padStart における padSize の求め方です。
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2019-01-14 16:24:19 +09:00
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$$
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\textrm{padSize} = \lceil \log_{10}(\mathbf{arraySize} + 1) \rceil
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$$
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```js
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2021-01-21 21:45:05 +09:00
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const padSize = Math.ceil(Math.log10(arr.length + 1));
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2019-01-14 16:24:19 +09:00
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2019-01-14 16:25:48 +09:00
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arr.forEach((item, index) => {
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2021-01-21 21:45:05 +09:00
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console.log(`${index.padStart(padSize, "0")}: ${item}`);
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});
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2019-01-14 16:24:19 +09:00
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```
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結果は以下のようになる。
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```
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01: item1
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02: item2
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03: item3
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04: item4
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05: item5
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06: item6
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07: item7
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08: item8
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09: item9
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10: item10
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```
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