How to upload array of images with axios?

Question

I have a React component in which a user can upload an unlimited number of images, which are collected in an array.

I am currently using FormData to upload these images, along with some other text fields.

However I want to get away from using FormData. Is there a better way to upload data like an array of images with plain Axios?

Component's State After 3 Image Uploads

this.state.files = [
   // image file 0,
   // image file 1,
   // image file 2
];

Current Axios Function - Using FormData

let formData = new FormData();

this.state.files.forEach(file => formData.append('files[]',file));

let headers = { 'Content-Type': "multipart/form-data; charset=utf-8; boundary=" + Math.random().toString().substr(2) };

axios.post('/api/upload-images',formData,{headers: headers});

Desired Axios Function - No FormData

let headers = { 'Content-Type': "multipart/form-data; charset=utf-8; boundary=" + Math.random().toString().substr(2) };

axios.post('/api/upload-images',{...this.state},{headers: headers});

When I try to do it in the desired way, the files on received by the server are empty.

THis might help stackoverflow.com/questions/47630163/…

Srikanth Gowda
– Srikanth Gowda

2020-01-16 13:43:09 +00:00
Commented Jan 16, 2020 at 13:43 — Srikanth Gowda
– Srikanth Gowda, Commented Jan 16, 2020 at 13:43

Patrick Stephansen · Accepted Answer · 2020-01-16 13:58:06Z

You could create a custom axios instance and set the transformRequest config parameter to a function that converts the data to a form when the multipart/form-data content type header is present. This would look something like the following. Disclaimer: I have not tested this.

// put formAxios in its own module to reuse it across the project
export const formAxios = axios.create({
    transformRequest: [function (data, headers) {
        if (headers['Content-Type'] && headers['Content-Type'].startsWith('multipart/form-data')) {
            const form = new FormData();
            for (const key in data) {
                const value = data[key];
                if (Array.isArray(value)) {
                    const arrayKey = `${key}[]`;
                    value.forEach(v => {
                        form.append(arrayKey, v);
                    });
                } else{
                    form.append(key, value);
                }
            }
            return form;
        }

        return data;
    }],
});

Calling this would be exactly like your last sample, but with the custom axios instance:

let headers = { 'Content-Type': "multipart/form-data; charset=utf-8; boundary=" + Math.random().toString().substr(2) };

formAxios.post('/api/upload-images', {...this.state}, {headers});

This is a great solution. I don't mind making this module once and then reusing it as you suggested.

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How to upload array of images with axios?

Component's State After 3 Image Uploads

Current Axios Function - Using FormData

Desired Axios Function - No FormData

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Component's State After 3 Image Uploads

Current Axios Function - Using FormData

Desired Axios Function - No FormData

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