本文描述了使用javascript读取用户通过Input控件选择的文件的内容的方法和注意事项。后面用英文写，但我的英文不太好，如有错误之处，希望大家帮我纠正，我的联系方式在后面。
When user select a file by <input type=file>, its content can be read by javascript like this:37Please respect copyright.ＰＥＮＡＮＡimc453InXG
---read whole file content into array buffer---37Please respect copyright.ＰＥＮＡＮＡi1iJTZ8Jr8
let file=input.files[0]; const reader = new FileReader(); 37Please respect copyright.ＰＥＮＡＮＡulpAZUJBD7
reader.onload = () => 37Please respect copyright.ＰＥＮＡＮＡselGXutMwV
{37Please respect copyright.ＰＥＮＡＮＡE0hyO2qj6z
let content_whole = new Uint8Array(reader.result);37Please respect copyright.ＰＥＮＡＮＡtFbFdbD5uE
}37Please respect copyright.ＰＥＮＡＮＡhnhfije6MZ
reader.readAsArrayBuffer(file);37Please respect copyright.ＰＥＮＡＮＡwGRVsu0gMZ
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If the file size is too large, the browser may crash as the whole file content are loaded into memory by array buffer. In order to avoid it, we can just read a part of the file like this:37Please respect copyright.ＰＥＮＡＮＡBIkdAopiVN
---read part of file content into array buffer---37Please respect copyright.ＰＥＮＡＮＡ4ImDUKgotV
let file=input.files[0], block_size=1000000, start=0, end=block_size; const reader = new FileReader(); 37Please respect copyright.ＰＥＮＡＮＡwO5PZ5LJ7L
reader.onload = () => 37Please respect copyright.ＰＥＮＡＮＡ3JjjUcN0a8
{37Please respect copyright.ＰＥＮＡＮＡSAg93WymdU
let content_part = new Uint8Array(reader.result);37Please respect copyright.ＰＥＮＡＮＡ7HjO5CxZ6j
}37Please respect copyright.ＰＥＮＡＮＡWi5J3tcQkg
reader.readAsArrayBuffer(file.slice(start,end));37Please respect copyright.ＰＥＮＡＮＡBq3WbxoG51
-----------------------------------------------
37Please respect copyright.ＰＥＮＡＮＡMWWsPMKOM9
Section X. Thanks37Please respect copyright.ＰＥＮＡＮＡLeDEUuLFfS
https://segmentfault.com/a/1190000022113605
Section Y. Contacts Me
If you found any errors or have any suggestions for this article, please let me know, my wechat: si_jinmin, my email: si.jinmin@gmail.com37Please respect copyright.ＰＥＮＡＮＡOXKZ25y87j
如果您发现本文有任何错误，或者对本文有好的建议，欢迎与我联系探讨，我的微信: si_jinmin, 我的email: si.jinmin@gmail.com
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