如何确定用户是否选择了文件上传文件？-Howtodetermineifuserselectedafileforfileupload?

89  

This works in IE (and FF, I believe):

这适用于IE（和FF，我相信）：

if(document.getElementById("uploadBox").value != "") {
   // you have a file
}

5  

this piece of code works in my local environment, hope it will also works in live

这段代码在我的本地环境中工作，希望它也能在现场工作

var nme = document.getElementById("uploadFile");
if(nme.value.length <4) {
    alert('Must Select any of your photo for upload!');
    nme.focus();
    return false;
}

0  

function validateAndUpload(input){
    var URL = window.URL || window.webkitURL;
    var file = input.files[0];

    if (file) {
        var image = new Image();

        image.Onload= function() {
            if (this.width) {
                 console.log('Image has width, I think it is real image');
                 //TODO: upload to backend
            }
        };

        image.src = URL.createObjectURL(file);
    }
};​

Call this function on change .

更改时调用此函数。

0  

You can use:

您可以使用：

    var files = uploadFile.files;

    if (files.length == 0) { console.log(true) } else { console.log(false) }
    if (files[0] == undefined) { console.log(true) } else { console.log(false) }
    if (files[0] == null) { console.log(true) } else { console.log(false) }

All three give the same result.

这三个都给出了相同的结果。