I am using react-dropzone to upload files.
<Dropzone
accept="image/jpeg"
multiple
onDrop={(acceptedFiles, rejectedFiles) => this.onDrop(acceptedFiles, rejectedFiles)}
/>
In the onDrop function, I scale each image that I get using canvas.
onDrop(acceptedFiles: Array<Object>, rejectedFiles: Array<Object>) {
if (acceptedFiles.length) {
const requestParams = {
parameters: {
generateContourImages: false,
},
images: [],
};
acceptedFiles.forEach(async (acceptedFile) => {
const { width, height } = await browserImageSize(acceptedFile);
const imagedata = await this.scaleImage(acceptedFile, width, height);
requestParams.images.push({
imagedata,
methods: methods,
imageID: uuidv4(),
});
});
} else {
this.setState({ error: true });
}
}
The actual scaling happens in the function below
async scaleImage(fileImage: Object, originalWidth: number, originalHeight: number) {
return new Promise((resolve) => {
const imageURL = URL.createObjectURL(fileImage);
const image = new Image();
image.onload = () => {
const scaleFactor = Math.max(originalWidth, originalHeight) / 1000;
const canvas = document.createElement('canvas');
canvas.width = originalWidth;
canvas.height = originalHeight;
const scaledWidth = Math.floor(originalWidth / scaleFactor);
const scaledHeight = Math.floor(originalHeight / scaleFactor);
const ctx = canvas.getContext('2d');
ctx.drawImage(image, 0, 0, scaledWidth, scaledHeight);
const base64 = canvas.toDataURL('image/jpeg');
resolve(base64.substr(23));
}
image.src = imageURL;
});
}
The requestParams
object that I construct will then be send to the server. My problem is that I want my client-side code to wait till it goes through all the images and constructs the final requestParams
object. That's not the case now. How do I make the above piece of code wait?
It can be achieved in the following manner:
async constructRequestParams(acceptedFiles: Array<Object>) {
return new Promise((resolve) => {
const requestParams = {
parameters: {
generateContourImages: false,
},
images: [],
};
acceptedFiles.forEach(async (acceptedFile, index) => {
const { width, height } = await browserImageSize(acceptedFile);
const imagedata = await this.scaleImage(acceptedFile, width, height);
requestParams.images.push({
imagedata,
methods: methods,
imageID: uuidv4(),
});
if (requestParams.images.length === acceptedFiles.length) {
resolve(requestParams);
}
});
})
}
async onDrop(acceptedFiles: Array<Object>, rejectedFiles: Array<Object>) {
if (acceptedFiles.length) {
const requestParams = await this.constructRequestParams(acceptedFiles);
} else {
this.setState({ error: true });
}
}