Tips for uploading a file using Axios in a form

Question

Tips for uploading a file using Axios in a form

When uploading a file to a Flask server, I can access files from the flask request global by using raw HTML with the following code:

<form id="uploadForm" action='upload_file' role="form" method="post" enctype=multipart/form-data>
    <input type="file" id="file" name="file">
    <input type=submit value=Upload>
</form>

In Flask:

def post(self):
    if 'file' in request.files:
        ....

However, when trying to achieve the same result with Axios, the flask request global is empty:

<form id="uploadForm" enctype="multipart/form-data" v-on:change="uploadFile">
<input type="file" id="file" name="file">
</form>

uploadFile: function (event) {
    const file = event.target.files[0]
    axios.post('upload_file', file, {
        headers: {
          'Content-Type': 'multipart/form-data'
        }
    })
}

If I remove the headers json from the axios.post method in the uploadFile function above, the form key of my flask request object contains a comma-separated list of string values since the file is a .csv. So how can I send a file object via axios?

javascript ajax file-upload axios

Answer 1

Answer №1

To upload the file, you need to add it to a formData object and make sure to include the Content-Type header set to multipart/form-data.

let formData = new FormData();
let fileInput = document.querySelector('#file');
formData.append("file", fileInput.files[0]);
axios.post('upload_endpoint', formData, {
    headers: {
      'Content-Type': 'multipart/form-data'
    }
})

Answer 2

To upload the file, you need to add it to a formData object and make sure to include the Content-Type header set to multipart/form-data.

let formData = new FormData();
let fileInput = document.querySelector('#file');
formData.append("file", fileInput.files[0]);
axios.post('upload_endpoint', formData, {
    headers: {
      'Content-Type': 'multipart/form-data'
    }
})

Answer 3

Answer №2

An example Vue application that needs a local backend server to process requests:

const app = new Vue({
  el: "#app",
  data: {
    file: ''
  },
  methods: {
    submitFile() {
      let formData = new FormData();
      formData.append('file', this.file);
      console.log('>> formData >> ', formData);

      // Requires a backend REST API 
      axios.post('http://localhost:8080/restapi/fileupload',
          formData, {
            headers: {
              'Content-Type': 'multipart/form-data'
            }
          }
        ).then(function () {
          console.log('SUCCESS!!');
        })
        .catch(function () {
          console.log('FAILURE!!');
        });
    },
    handleFileUpload() {
      this.file = this.$refs.file.files[0];
      console.log('>>>> 1st element in files array >>>> ', this.file);
    }
  }
});

Link to Example

Answer 4

An example Vue application that needs a local backend server to process requests:

const app = new Vue({
  el: "#app",
  data: {
    file: ''
  },
  methods: {
    submitFile() {
      let formData = new FormData();
      formData.append('file', this.file);
      console.log('>> formData >> ', formData);

      // Requires a backend REST API 
      axios.post('http://localhost:8080/restapi/fileupload',
          formData, {
            headers: {
              'Content-Type': 'multipart/form-data'
            }
          }
        ).then(function () {
          console.log('SUCCESS!!');
        })
        .catch(function () {
          console.log('FAILURE!!');
        });
    },
    handleFileUpload() {
      this.file = this.$refs.file.files[0];
      console.log('>>>> 1st element in files array >>>> ', this.file);
    }
  }
});

Link to Example

Answer 5

Answer №3

If your API has specific content-type requirements and doesn't accept multipart/formdata, you can opt for an alternative approach to uploading files:

handleFileUpload: function (event) {
    const file = event.target.files[0]
    axios.post('upload_file', file, {
        headers: {
          'Content-Type': file.type
        }
    })
}

Answer 6

If your API has specific content-type requirements and doesn't accept multipart/formdata, you can opt for an alternative approach to uploading files:

handleFileUpload: function (event) {
    const file = event.target.files[0]
    axios.post('upload_file', file, {
        headers: {
          'Content-Type': file.type
        }
    })
}

Answer 7

Answer №4

Exploring React and working with HTML input elements

Understanding how to create an input field in HTML

<input type="file" onChange={onChange} accept ="image/*"/>

Implementing an onChange listener for the input field

const onChange = (e) => {
  let url = "https://<server-url>/api/upload";
  let file = e.target.files[0];
  uploadFile(url, file);
};

const uploadFile = (url, file) => {
  let formData = new FormData();
  formData.append("file", file);
  axios.post(url, formData, {
      headers: {
        "Content-Type": "multipart/form-data",
      },
    }).then((response) => {
      handleSuccess(response);
    }).catch((error) => {
      handleFail(error);
    });
};

const handleSuccess = (response) => {
  //Implement success handling logic here
};

const handleFail = (error) => {
  //Implement failure handling logic here
};

Answer 8

Exploring React and working with HTML input elements

Understanding how to create an input field in HTML

<input type="file" onChange={onChange} accept ="image/*"/>

Implementing an onChange listener for the input field

const onChange = (e) => {
  let url = "https://<server-url>/api/upload";
  let file = e.target.files[0];
  uploadFile(url, file);
};

const uploadFile = (url, file) => {
  let formData = new FormData();
  formData.append("file", file);
  axios.post(url, formData, {
      headers: {
        "Content-Type": "multipart/form-data",
      },
    }).then((response) => {
      handleSuccess(response);
    }).catch((error) => {
      handleFail(error);
    });
};

const handleSuccess = (response) => {
  //Implement success handling logic here
};

const handleFail = (error) => {
  //Implement failure handling logic here
};

Answer 9

Answer №5

Hopefully this solution will be useful for others too.

const form = $('#form');
let formData = new FormData(form[0]);
axios.post('your-url', formData)
    .then(response => {
        console.log({response});
    }).catch(error => {
        console.error({error});
    });

Answer 10

Hopefully this solution will be useful for others too.

const form = $('#form');
let formData = new FormData(form[0]);
axios.post('your-url', formData)
    .then(response => {
        console.log({response});
    }).catch(error => {
        console.error({error});
    });

Answer 11

Answer №6

Here is the method I prefer:

let data = new FormData(formElement);
//data.append("image", imageFile.files[0]);
const response = await axios.post(
  "link-handle",
  data,
  {
    headers: {
      "Content-Type": "multipart/form-data",
    },
  }
);

Answer 12

Here is the method I prefer:

let data = new FormData(formElement);
//data.append("image", imageFile.files[0]);
const response = await axios.post(
  "link-handle",
  data,
  {
    headers: {
      "Content-Type": "multipart/form-data",
    },
  }
);

Answer 13

Answer №7

Here is a guide on how to upload a file using an object in memory, such as a JSON object:

import axios from 'axios';
import * as FormData  from 'form-data'

async function sendData(jsonData){
    // const payload = JSON.stringify({ hello: 'world'});
    const payload = JSON.stringify(jsonData);
    const bufferObject = Buffer.from(payload, 'utf-8');
    const file = new FormData();

    file.append('upload_file', bufferObject, "b.json");

    const response = await axios.post(
        lovelyURL,
        file,
        headers: file.getHeaders()
    ).toPromise();


    console.log(response?.data);
}

Answer 14

Here is a guide on how to upload a file using an object in memory, such as a JSON object:

import axios from 'axios';
import * as FormData  from 'form-data'

async function sendData(jsonData){
    // const payload = JSON.stringify({ hello: 'world'});
    const payload = JSON.stringify(jsonData);
    const bufferObject = Buffer.from(payload, 'utf-8');
    const file = new FormData();

    file.append('upload_file', bufferObject, "b.json");

    const response = await axios.post(
        lovelyURL,
        file,
        headers: file.getHeaders()
    ).toPromise();


    console.log(response?.data);
}

Answer 15

Answer №8

When using Axios version 0.25.0 > up to 0.27.2, there seems to be a problem with handling the FormData object in a PUT request if more than one field has been appended. However, the request works fine when only one field contains a file.

Additionally, starting from Axios version 0.25.0, the correct headers are automatically set, eliminating the need to specify the Content-Type.

Answer 16

When using Axios version 0.25.0 > up to 0.27.2, there seems to be a problem with handling the FormData object in a PUT request if more than one field has been appended. However, the request works fine when only one field contains a file.

Additionally, starting from Axios version 0.25.0, the correct headers are automatically set, eliminating the need to specify the Content-Type.

Answer 17

Answer №9

When capturing a photo, it is important to save the image and remember its location. Afterwards, retrieve the image's binary large object (blob) from its stored location on the machine. Then, include the blob in a formData object along with the image's name. Finally, send a request with the header set to 'multipart/form-data', causing the image to be found in the backend under 'req.files'.

Answer 18

When capturing a photo, it is important to save the image and remember its location. Afterwards, retrieve the image's binary large object (blob) from its stored location on the machine. Then, include the blob in a formData object along with the image's name. Finally, send a request with the header set to 'multipart/form-data', causing the image to be found in the backend under 'req.files'.

Answer 19

Answer №10

It took me some time to realize that the error in my controller was due to the actual parameter name... This discovery may assist someone else in a similar situation. I am utilizing Next.js / .Net 6.

Client:

export const test = async (event: any) => {
    const token = useAuthStore.getState().token;
    console.log(event + 'the event')
    if (token) {
        const formData = new FormData();
        formData.append("img", event);
        const res = await axios.post(baseUrl + '/products/uploadproductimage', formData, {
            headers: {
                'Authorization': `bearer ${token}`
            }
        })
        return res
    }
    return null
}

Server:

 [HttpPost("uploadproductimage")]
        public async Task<ActionResult> UploadProductImage([FromForm] IFormFile image)
        {
            return Ok();
        }

The error occurred because the server expected the parameter to be named "image" instead of "img":

formData.append("img", event);

public async Task<ActionResult> UploadProductImage([FromForm] IFormFile image)

Answer 20

It took me some time to realize that the error in my controller was due to the actual parameter name... This discovery may assist someone else in a similar situation. I am utilizing Next.js / .Net 6.

Client:

export const test = async (event: any) => {
    const token = useAuthStore.getState().token;
    console.log(event + 'the event')
    if (token) {
        const formData = new FormData();
        formData.append("img", event);
        const res = await axios.post(baseUrl + '/products/uploadproductimage', formData, {
            headers: {
                'Authorization': `bearer ${token}`
            }
        })
        return res
    }
    return null
}

Server:

 [HttpPost("uploadproductimage")]
        public async Task<ActionResult> UploadProductImage([FromForm] IFormFile image)
        {
            return Ok();
        }

The error occurred because the server expected the parameter to be named "image" instead of "img":

formData.append("img", event);

public async Task<ActionResult> UploadProductImage([FromForm] IFormFile image)

Tips for uploading a file using Axios in a form

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

Answer №8

Answer №9

Answer №10

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