how to assign value of readAsDataURL() to a variable?

问题

okay so I've seen many examples and questions on using readAsDataURL(), but none of them seem to resolve my issue. Following is my code :

$(document).ready(function(){
    var fileReader = new FileReader();
    $("form").submit(function(e){
        e.preventDefault();
        console.log(fileReader.readAsDataURL(document.getElementById("userfile").files[0]));
    });
});

what i get in console is undefined . I'm trying to get the base64 encoded file data on a variable so that i can upload it using ajax. Can anyone tell me what i am doing wrong?

回答1:

Most methods of a FileReader instance report the results asynchronously.

You have to bind an onload event to capture the result:

var fileReader = new FileReader();
fileReader.onload = function(event) {
    console.log(event.target.result);
};
fileReader.readAsDataURL(document.getElementById("userfile").files[0]);

来源：https://stackoverflow.com/questions/15998610/how-to-assign-value-of-readasdataurl-to-a-variable