The readAsDataURL
method is used to read the contents of the specified Blob
or File
. When the read operation is finished, the readyState
becomes DONE
, and the loadend
is triggered. At that time, the result
attribute contains the data as a data: URL representing the file's data as a base64 encoded string.
Note: The blob's result
cannot be directly decoded as Base64 without first removing the Data-URL declaration preceding the Base64-encoded data. To retrieve only the Base64 encoded string, first remove data:*/*;base64,
from the result.
HTML
<input type="file" onchange="previewFile()" /><br />
<img src="" height="200" alt="Image preview" />
JavaScript
function previewFile() {
const preview = document.querySelector("img");
const file = document.querySelector("input[type=file]").files[0];
const reader = new FileReader();
reader.addEventListener(
"load",
() => {
preview.src = reader.result;
},
false,
);
if (file) {
reader.readAsDataURL(file);
}
}
Result
HTML
<input id="browse" type="file" multiple />
<div id="preview"></div>
JavaScript
function previewFiles() {
const preview = document.querySelector("#preview");
const files = document.querySelector("input[type=file]").files;
function readAndPreview(file) {
if (/\.(jpe?g|png|gif)$/i.test(file.name)) {
const reader = new FileReader();
reader.addEventListener(
"load",
() => {
const image = new Image();
image.height = 100;
image.title = file.name;
image.src = reader.result;
preview.appendChild(image);
},
false,
);
reader.readAsDataURL(file);
}
}
if (files) {
Array.prototype.forEach.call(files, readAndPreview);
}
}
const picker = document.querySelector("#browse");
picker.addEventListener("change", previewFiles);
Result