回答編集履歴
2
FileList.prototype.length
test
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@@ -40,6 +40,74 @@
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### FileList.prototype.length
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FileList InterfaceのIDLは下記の通り。
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- [5. FileList インタフェース - File API （日本語訳）](https://triple-underscore.github.io/File_API-ja.html#filelist-section)
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> ```
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> [Exposed=(Window,Worker), Serializable]
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> interface FileList {
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> getter File? item(unsigned long index);
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> readonly attribute unsigned long length;
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> };
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> ```
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Google Chromeでも `FileList.prototype.length` に getter が定義されていることを確認できます。
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- [Object.prototype.hasOwnProperty() - JavaScript | MDN](https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwnProperty)
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- [Object.getOwnPropertyDescriptor() - JavaScript | MDN](https://developer.mozilla.org/ja/docs/Web/JavaScript/Reference/Global_Objects/Object/getOwnPropertyDescriptor)
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```HTML
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<input id="sample" type="file">
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<script>
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'use strict';
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const files = document.getElementById('sample').files;
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const filesPrototype = Object.getPrototypeOf(files);
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console.log(filesPrototype === FileList.prototype); // true
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console.log(files.hasOwnProperty('length')); // false
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console.log(filesPrototype.hasOwnProperty('length')); // true
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console.log(Object.getOwnPropertyDescriptor(filesPrototype, 'length')); // {set: undefined, enumerable: true, configurable: true, get: ƒ}
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</script>
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```
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### プロトタイプチェーン
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1
FileList -> FileList.prototype
test
CHANGED
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@@ -2,7 +2,7 @@
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`HTMLInputElement.prototype.files` を参照すれば、「`FileList` を `[[Prototype]]` に持つオブジェクト」を返します。
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`HTMLInputElement.prototype.files` を参照すれば、「`FileList.prototype` を `[[Prototype]]` に持つオブジェクト」を返します。
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