Is there a way to verify if a FormData file has no content?

Question

Is there a way to verify if a FormData file has no content?

Currently working on an AJAX form where users can choose a background color or upload a background image. The aim is to have the bgColor field ignored if a file is specified for bgImg.

<label>Color: <input type="color" name="bgColor" value="#000000"></label><br>
<label>Image: <input type="file" name="bgImg" accept="image/png"></label><br>

I thought using the FormData API would be the simplest way to collect the form data:

var fd = new FormData(document.getElementById('myForm'));

The issue arises when trying to determine if a file has been selected in the FormData object. When checking fd.has('bgImg'), it returns true regardless of whether a file is actually selected, which makes sense because the field exists.

However, when attempting to check with fd.get('bgImg'), my browser crashes if no file is selected. This creates a situation where determining if the bgImg field is empty becomes impossible. So, what is the correct approach in this case?

While I could use elements['bgImg'].files from the form, I prefer sticking to the FormData API for its simplicity and cleanliness. Is there a reason why it seems to malfunction in this scenario? Is checking the files collection the only viable solution?

UPDATE: It appears that the FormData API may not have strong browser support outside of Firefox, so relying on element.files might be a more reliable option. However, the unexpected crashing in Firefox remains a mystery. If no explanation is found soon, I might provide my own solution.

javascript ajax forms

Answer 1

Answer №1

It appears that the behavior of the FormData API in Firefox could potentially be a bug. However, considering the limited support for FormData methods in various browsers, it may be more reliable to check form elements directly:

const formElements = document.getElementById('mandelForm').elements;
console.log(formElements['bgImg'].files.length > 0); // Returns true if file is selected

Answer 2

It appears that the behavior of the FormData API in Firefox could potentially be a bug. However, considering the limited support for FormData methods in various browsers, it may be more reliable to check form elements directly:

const formElements = document.getElementById('mandelForm').elements;
console.log(formElements['bgImg'].files.length > 0); // Returns true if file is selected

Answer 3

Answer №2

Simple method:

let formData = new FormData();
console.log(!!formData.entries().next().value); // false
formData.append("bar", 'yyy')
console.log(!!formData.entries().next().value); // true

Answer 4

Simple method:

let formData = new FormData();
console.log(!!formData.entries().next().value); // false
formData.append("bar", 'yyy')
console.log(!!formData.entries().next().value); // true

Answer 5

Answer №3

formData = new FormData();
for (let j = 0 ; j < files.length ; j ++){
      if(files[j].size > 0)
      {
            formData.append('file', files[j]);
      }
}

Answer 6

formData = new FormData();
for (let j = 0 ; j < files.length ; j ++){
      if(files[j].size > 0)
      {
            formData.append('file', files[j]);
      }
}

Is there a way to verify if a FormData file has no content?

Answer №1

Answer №2

Answer №3

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