for loop fetch api call and store responses in an state array reactjs

Question

getTarget(filepath){
 const filepaths = [target1, target2, target3, target4]

 for (var i =0; i< filepaths.length; i++){
   var filepath = filepaths[i]
   fetch(filepath)
      .then((response) => response.blob())
      .then(data => { 
        var reader = new FileReader();
        reader.readAsDataURL(data); 
        reader.onloadend = (event)=> {
            var base64data = reader.result;
            this.setState(prevState => ({
               targetlist: prevState.targetlist.concat(base64data)
            }))           
        }
      });
    }

Target 1-4 are images that I have to convert into base64 and stored in the web app in ordered array. I am able to store the 4 images into the targetlist state. However, the order will be all jumbled up. How do I ensure that the list will not be jumbled up from the different time that the responses return?

Or is there a better method that I am able to get the base64 string. The images are stored in local memory.

Answer 1

You can use async/await like this

async function getTarget(filepath) {
 const filepaths = [target1, target2, target3, target4]
 for (let i =0; i< filepaths.length; i+=1){
   const filepath = filepaths[i]
   const data = await (await fetch(filepath)).blob();
   const reader = new FileReader();
   reader.readAsDataURL(data); 
   reader.onloadend = (event) => {
        const base64data = reader.result;
        this.setState(prevState => ({
           targetlist: prevState.targetlist.concat(base64data)
        }))
   }
 }
}

Answer 2

getTarget(filepath){
 const filepaths = [target1, target2, target3, target4]

 for (var i =0; i< filepaths.length; i++){
   var filepath = filepaths[i]
   fetch(filepath)
      .then((response) => [i, response.blob()])
      .then(data => { 
        var reader = new FileReader();
        reader.readAsDataURL(data[1]); 
        reader.onloadend = (event)=> {
            var base64data = reader.result;
            this.setState(prevState => ({
               ...prevState,
               // just replace that index's value - so that list will be ordered.
               targetlist: prevState.targetlist.map((item, index) => (index===i) ? base64data : item)
            }))           
        }
      });
 }
}