Can Javascript upload multiple images & convert them to base64?

user2931494
May 11, 2023
97 views
1 vote
2 Answers

I’m trying to create a form where you can upload multiple images using two file inputs, see the images as base64 and later submit them using jQuery’s POST. The problem is that when I select 3 different images, I see only the last one 3 times. I guess the problem is in the for in the addEventListener – maybe it’s not in the right place?

<div class="form-group">
    <label for="product_photo_1">Photos 1</label>
    <div class="custom-file">
        <input type="file" class="custom-file-input" id="product_photo_1" multiple />
        <label class="custom-file-label" for="product_photo_1" data-browse="Select">Please, select a file...</label>
    </div>
    <div id="product_photo_1_result"></div>
</div>
<div class="form-group">
    <label for="product_photo_2">Photos 2</label>
    <div class="custom-file">
        <input type="file" class="custom-file-input" id="product_photo_2" multiple />
        <label class="custom-file-label" for="product_photo_2" data-browse="Select">Please, select a file...</label>
    </div>
    <div id="product_photo_2_result"></div>
</div>
<script>
    const convertBase64 = (file) => {
        return new Promise((resolve, reject) => {
            const fileReader = new FileReader();

            fileReader.readAsDataURL(file);

            fileReader.onload = () => {
                resolve(fileReader.result);
            };

            fileReader.onerror = (error) => {
                reject(error);
            };
        });
    };

    const uploadImage = async (event, id) => {
        const file = event.target.files[0];

        const base64 = await convertBase64(file);

        document.getElementById("product_photo_" + id + "_result").innerHTML += '<img src="' + base64 + '" class="img-thumbnail m-2" id="product_photo_' + id + '[]" style="height: 50px;" />';
    };

    document.getElementById("product_photo_1").addEventListener("change", (event) => {
        for(var index = 1; index <= document.getElementById("product_photo_1").files.length; index++) {
            uploadImage(event, 1);
        }
    });

    document.getElementById("product_photo_2").addEventListener("change", (event) => {
        for(var index = 1; index <= document.getElementById("product_photo_2").files.length; index++) {
            uploadImage(event, 2);
        }
    });
</script>

Tags: javascript

Answers

In uploadImage function you are passing event argument and select first file every time

const file = event.target.files[0];

Instead you can pass files one by one to the uploadImage.

Here is the example:

<div class="form-group">
  <label for="product_photo_1">Photos 1</label>
  <div class="custom-file">
    <input type="file" class="custom-file-input" id="product_photo_1" multiple />
    <label class="custom-file-label" for="product_photo_1" data-browse="Select">Please, select a file...</label>
  </div>
  <div id="product_photo_1_result"></div>
</div>
<div class="form-group">
  <label for="product_photo_2">Photos 2</label>
  <div class="custom-file">
    <input type="file" class="custom-file-input" id="product_photo_2" multiple />
    <label class="custom-file-label" for="product_photo_2" data-browse="Select">Please, select a file...</label>
  </div>
  <div id="product_photo_2_result"></div>
</div>
<script>
  const convertBase64 = (file) => {
    return new Promise((resolve, reject) => {
      const fileReader = new FileReader();

      fileReader.readAsDataURL(file);

      fileReader.onload = () => {
        resolve(fileReader.result);
      };

      fileReader.onerror = (error) => {
        reject(error);
      };
    });
  };

  const uploadImage = async (file, id) => {
  
    const base64 = await convertBase64(file);

    document.getElementById("product_photo_" + id + "_result").innerHTML += '<img src="' + base64 + '" class="img-thumbnail m-2" id="product_photo_' + id + '[]" style="height: 50px;" />';
  };

  document.getElementById("product_photo_1").addEventListener("change", (event) => {
   let files = document.getElementById("product_photo_1").files;
    for (let index = 0; index <= files.length; index++) {
      uploadImage(files[index], 1);
    }
  });

  document.getElementById("product_photo_2").addEventListener("change", (event) => {
    let files = document.getElementById("product_photo_2").files;
    for (let index = 0; index <= document.getElementById("product_photo_2").files.length; index++) {
      uploadImage(files[index], 2);
    }
  });

</script>

In the event handlers, you are doing a loop, but you are not using the value of index per iteration:

    document.getElementById("product_photo_1").addEventListener("change", (event) => {
        for(var index = 1; index <= document.getElementById("product_photo_1").files.length; index++) {
            uploadImage(event, 1); //passing only the event and an index
        }
    });

    document.getElementById("product_photo_2").addEventListener("change", (event) => {
        for(var index = 1; index <= document.getElementById("product_photo_2").files.length; index++) {
            uploadImage(event, 2); //passing only the event and the index
        }
    });

And now, let's use `index` for all calls as well as clearing up when it's 0:

const uploadImage = async (event, id, index) => {
    let context = document.getElementById("product_photo_" + id + "_result");
    const file = event.target.files[index]; //we get the correct file;

    const base64 = await convertBase64(file);

    let template = '<img src="' + base64 + '" class="img-thumbnail m-2" id="product_photo_' + id + '[]" style="height: 50px;" />';

    if (index === 0) context.innerHTML = template; //clearing older values and adding the first element
    else context.innerHTML += template; //appending the (not first) element
};

Instead, you will need to pass the index as well, like this:

    document.getElementById("product_photo_1").addEventListener("change", (event) => {
        for(var index = 0; index < document.getElementById("product_photo_1").files.length; index++) {
            uploadImage(event, 1, index);
        }
    });

    document.getElementById("product_photo_2").addEventListener("change", (event) => {
        for(var index = 0; index < document.getElementById("product_photo_2").files.length; index++) {
            uploadImage(event, 2, index);
        }
    });

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