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Preview an image before uploading it

Written byPhuoc Nguyen
Category
Level 2 — Intermediate
Created
21 Feb, 2020
We prepare the markup for a file input which allows to choose an image, and an `img` element for previewing the selected file.
<input type="file" id="fileInput" />

<img id="preview" />
Both elements can be taken by the `getElementById()` method:
const fileEle = document.getElementById('fileInput');
const previewEle = document.getElementById('preview');

1. Use the URL.createObjectURL() method

fileEle.addEventListener('change', function (e) {
// Get the selected file
const file = e.target.files[0];

// Create a new URL that references to the file
const url = URL.createObjectURL(file);

// Set the source for preview element
previewEle.src = url;
});

2. Use the FileReader's readAsDataURL() method

fileEle.addEventListener('change', function (e) {
// Get the selected file
const file = e.target.files[0];

const reader = new FileReader();
reader.addEventListener('load', function () {
// Set the source for preview element
previewEle.src = reader.result;
});

reader.readAsDataURL(file);
});

See also

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Phước Nguyễn