使用 JavaScript 的 FileReader 接口时检测文件的内容类型
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/4264289/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Detecting a file's content-type when using JavaScript's FileReader interface
提问by u365975
I've been setting up an import script for plain-text files in a web application.
我一直在为 Web 应用程序中的纯文本文件设置导入脚本。
My script is as follows:
我的脚本如下：
function dataImport(files) {
confirm("Are you sure you want to import the selected file? This will overwrite any data that is currently saved in the application workspace.");
for (i = 0; i < files.length; i++) {
file = files[i]
console.log(file)
var reader = new FileReader()
ret = []
reader.onload = function(e) {
window.localStorage.setItem("ApplicationData", e.target.result);
}
reader.onerror = function(stuff) {
console.log("error", stuff)
console.log (stuff.getMessage())
}
reader.readAsText(file)
}
}
It's essentially a modification of that posed on this question.
它本质上是对这个问题提出的修改。
However, at the moment the user can technically attempt to import any file. As it's designed for plain-text files, problems can arise if a different type of file is imported.
但是，目前用户可以在技术上尝试导入任何文件。由于它是为纯文本文件设计的，如果导入不同类型的文件，可能会出现问题。
I've noticed in the console that the browser detects the content-type of the file being imported. Here's an example.
我在控制台中注意到浏览器检测到正在导入的文件的内容类型。这是一个例子。
fileName: "ideas.txt"
fileSize: 377
name: "ideas.txt"
size: 377
type: "text/plain"
webkitRelativePath: ""
Is it possible, then, to set up an argument where the script detects the content-type of the file, and if it isn't one of a number of specified suitable content-types, have the script refuse to import it?
那么，是否可以设置一个参数，让脚本检测文件的内容类型，如果它不是许多指定的合适内容类型之一，脚本是否拒绝导入它？
Thanks in advance for any advice.
提前感谢您的任何建议。
回答by trembl
if (file.type.match('text/plain')) {
// file type is text/plain
} else {
// file type is not text/plain
}
String.match is a RegEx, so if you would want to check, if the file is any type of text, you could do that:
String.match 是一个 RegEx，所以如果你想检查文件是否是任何类型的文本，你可以这样做：
if (file.type.match('text.*')) {
// file type starts with text
} else {
// file type does not start with text
}
回答by Benny Neugebauer
The Content Type can be read with the following code:
可以使用以下代码读取内容类型：
// Note: File is a file object than can be read by the HTML5 FileReader API
var reader = new FileReader();
reader.onload = function(event) {
var dataURL = event.target.result;
var mimeType = dataURL.split(",")[0].split(":")[1].split(";")[0];
alert(mimeType);
};
reader.readAsDataURL(file);
