回答編集履歴
6
a
test
CHANGED
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@@ -39,3 +39,7 @@
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`selectedWeeks`が配列であると仮定するならば、`Array.prototype.includes()`が使えるので調べて見てください。[https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Global_Objects/Array/includes](https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Global_Objects/Array/includes)
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なお、`String.prototype.includes()`も存在しているので、`selectedWeeks`が文字列の場合でも`includes`は使えます。
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5
a
test
CHANGED
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@@ -14,9 +14,9 @@
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const todo = {};
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-
todo.selectedWeeks.in
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+
todo.selectedWeeks.indexOf('monday')
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// => Uncaught TypeError: Cannot read property 'in
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// => Uncaught TypeError: Cannot read property 'indexOf' of undefined
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```
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@@ -26,9 +26,9 @@
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const todo = { selectedWeeks: undefined };
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todo.selectedWeeks.in
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todo.selectedWeeks.indexOf('monday')
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// => Uncaught TypeError: Cannot read property 'in
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// => Uncaught TypeError: Cannot read property 'indexOf' of undefined
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```
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4
a
test
CHANGED
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@@ -31,3 +31,11 @@
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// => Uncaught TypeError: Cannot read property 'includes' of undefined
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```
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35
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37
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> JSX上で「〜を含む」でindexOf()以外の方法を使う必要があるのでしょうか。
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39
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41
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`selectedWeeks`が配列であると仮定するならば、`Array.prototype.includes()`が使えるので調べて見てください。[https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Global_Objects/Array/includes](https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Global_Objects/Array/includes)
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3
a
test
CHANGED
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@@ -10,6 +10,8 @@
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10
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```
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// 1
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const todo = {};
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todo.selectedWeeks.includes('monday')
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@@ -17,3 +19,15 @@
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// => Uncaught TypeError: Cannot read property 'includes' of undefined
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```
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```
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// 2
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const todo = { selectedWeeks: undefined };
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todo.selectedWeeks.includes('monday')
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// => Uncaught TypeError: Cannot read property 'includes' of undefined
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```
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2
a
test
CHANGED
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@@ -3,3 +3,17 @@
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3
3
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4
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5
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現状、`console.log(todo.selectedWeeks)`とすると、`undefined`になるはずです。
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6
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7
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8
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9
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以下、簡易的なコードでの現象再現。
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10
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```
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12
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const todo = {};
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todo.selectedWeeks.includes('monday')
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// => Uncaught TypeError: Cannot read property 'includes' of undefined
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```
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1
a
test
CHANGED
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@@ -2,4 +2,4 @@
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2
2
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3
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4
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5
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`console.log(todo.selectedWeeks)`とすると、`undefined`になるはずです。
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5
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現状、`console.log(todo.selectedWeeks)`とすると、`undefined`になるはずです。
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