在< input>检查所选文件匹配接受属性标签

问题描述

我希望防止用户上传文件，服务器会从页面上以最少的JavaScript来拒绝文件，理想情况下不需要像jQuery那样增加任何重要的依赖关系，纯粹是为了解决这个问题。

因为我不是针对传统用户，所以我使用浏览器的表单验证系统来检查用户是否选择了一个有效的文件，但它似乎只关心用户是否选择文件而不管类型。

 > i = document.querySelector（'input [type = file]'）
< input type =fileaccept =image / *name =attachmentrequired> 
 > i.accept 
image / *
> i.files [0] .type 
application / x-zip-compressed
> i.checkValidity（）
 true 
  

有没有简单的方法来做到这一点？我唯一发现的就是，但它有点重量级的解决方案

解决方案

您可以执行RegExp测试 - 下面的代码转换MIME类型字符串中的通配符以匹配RegExp语法，这对输入文件的类型：

 （new RegExp（i.accept.replace（'*'，'.\ * '）））.test（i.files [0] .type）
  

。

编辑：

我已经问过这里的陌生人部分）。但是，这至少在Chrome 31中表现得如预期一样：

  void function enhanceFileInputTypeValidityCheck（）{
 var inputPrototype = document.createElement（'input'）.constructor.prototype; 
 var nativeCheckValidity = inputPrototype.checkValidity; 
 
 function validateFileInputType（input）{
 var MIMEtype = new RegExp（input.accept.replace（'*'，'.\ *'））; 
 
返回Array.prototype.every.call（input.files，函数passesAcceptedFormat（file）{
 return MIMEtype.test（file.type）; 
}）; 
 
 
函数validateInputs（）{
 Array.prototype.forEach.call（document.querySelectorAll（'input，select'），function callValidation（input）{
 input.checkValidity（）; 
}）; 
 
 
 inputPrototype.checkValidity = function enhancedCheckValidity（）{
 if（this.type ==='file'&& this.accept&&& this。文件&& this.files.length）{
 if（！validateFileInputType（this））{
 this.setCustomValidity（'请只提交'+ this.accept'类型的文件）; 
 
返回false; 
} 
} 
 
返回nativeCheckValidity.apply（this）; 
 
 
 Array.prototype.forEach.call（['change'，'input']，function bindValidation（event）{
 document.documentElement.addEventListener（event，validateInputs ）; 
}）; 
}（）; 
  

（尝试使用无效的文件类型提交）。

I wish to prevent the user from uploading a file the server will reject from a page with minimal JavaScript on it, ideally without adding any heavy dependencies like jQuery purely to solve this one problem.

Since I'm not targeting legacy users, I trued using the browser's form validation system to check if the user has selected a valid file, however it only seems to care if the user selects a file regardless of type.

> i = document.querySelector('input[type=file]')
<input type=​"file" accept=​"image/​*" name=​"attachment" required>​
> i.accept
"image/*"
> i.files[0].type
"application/x-zip-compressed"
> i.checkValidity()
true

Is there a simple way of doing this? The only thing that I have found that comes close is jQuery Validate, but it's a bit of a heavyweight solution.

解决方案

You could just perform a RegExp test — the following converts the wildcard in MIME type strings to match RegExp syntax, and tests that against the input file's type:

( new RegExp( i.accept.replace( '*', '.\*' ) ) ).test( i.files[ 0 ].type )

Demo here.

EDIT:

I eventually found a way to make this functionality seamless with native browser validation behaviour (ie prevent submission for invalid inputs, notify user using native validation warnings), but I'm not exactly sure how the code works or whether it's good practice (I've asked about the stranger parts here). However, this appears to behave as expected, at least in Chrome 31:

void function enhanceFileInputTypeValidityCheck(){
    var inputPrototype      = document.createElement( 'input' ).constructor.prototype;
    var nativeCheckValidity = inputPrototype.checkValidity;

    function validateFileInputType( input ){
        var MIMEtype = new RegExp( input.accept.replace( '*', '.\*' ) );

        return Array.prototype.every.call( input.files, function passesAcceptedFormat( file ){
            return MIMEtype.test( file.type );
        } );
    }

    function validateInputs(){
        Array.prototype.forEach.call( document.querySelectorAll( 'input, select' ), function callValidation( input ){
            input.checkValidity();
        } );
    }

    inputPrototype.checkValidity = function enhancedCheckValidity(){
        if( this.type === 'file' &&  this.accept && this.files && this.files.length ){
            if( !validateFileInputType( this ) ){
                this.setCustomValidity( 'Please only submit files of type ' + this.accept );

                return false;
            }
        }

        return nativeCheckValidity.apply( this );
    }

    Array.prototype.forEach.call( [ 'change', 'input' ], function bindValidation( event ){
        document.documentElement.addEventListener( event, validateInputs );
    } );
}();

Demo here (attempt to submit with an invalid file type).

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