回答編集履歴
2
誤字修正
test
CHANGED
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@@ -74,9 +74,9 @@
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74
74
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75
75
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for (let i = 0; i <= 5; i++) {
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76
76
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77
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-
if (array[i] === undefined) array[i] = [];
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77
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if (array_[i] === undefined) array_[i] = [];
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78
78
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79
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-
array[i].push('add');
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79
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array_[i].push('add');
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80
80
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81
81
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}
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82
82
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1
質問クローズを受けて追記
test
CHANGED
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@@ -17,3 +17,71 @@
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17
17
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}
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18
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19
19
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```
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20
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23
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###質問クローズを受けて追記
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24
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25
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26
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27
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jun68yktさんなどが挙げたスプレッド演算子を使って代入する方法は、破壊的なので、元のコードと微妙に振る舞いが違います。
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28
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+
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29
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あまり変わったことをしていなければ問題ないとは思いますが、お気を付けください。
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30
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31
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32
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33
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```js
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34
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35
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const array = [];
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36
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37
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38
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39
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array[0] = ['0'];
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40
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41
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array[1] = ['1'];
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42
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43
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array[3] = ['3'];
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44
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45
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const old = array[3];
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46
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47
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48
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49
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for (let i = 0; i <= 5; i++) {
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50
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51
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array[i] = [...(array[i] || []), 'add'];
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52
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53
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}
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54
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55
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56
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57
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console.table(old === array[3]); // false
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58
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59
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60
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61
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const array_ = [];
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62
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63
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64
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65
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array_[0] = ['0'];
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66
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67
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array_[1] = ['1'];
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68
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69
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array_[3] = ['3'];
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70
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71
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const old_ = array_[3];
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72
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73
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74
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75
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for (let i = 0; i <= 5; i++) {
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76
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77
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if (array[i] === undefined) array[i] = [];
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78
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79
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array[i].push('add');
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80
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81
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}
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82
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83
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84
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85
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console.table(old_ === array_[3]); // true
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86
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87
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```
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