How do I return the variable assigned by the asynchronous method within the function?

 const list = [
        "./img.png",//
        "//be-fe.github.io/static/images/iSlider-card/10.jpg",//
        "./load.gif",//
        "//be-fe.github.io/static/images/iSlider-card/12.jpg",//
        null,//
        "//be-fe.github.io/static/images/iSlider-card/17.jpg",//
        ];    
        const placeholder = "";
        const loadError = "";
        const gen = () => {
            let endSrc = placeholder;
            let html = "";
            list.forEach((ele) => {
                if(ele){
                    const image = new Image();
                    image.src = ele;
                    image.onload = () => {
                        endSrc = ele;
                    };
                    image.onerror = () => {
                        endSrc = loadError;
                    };
                }
               html += `
${endSrc}
`;
            });
            // html onload onerror[loaderror ]
            return html;
        }
        $("body").append(gen())

React.js node.js javascript
Jan.08,2022

use Promise 

const gen = () => {
  return Promise.all(list.map(ele => {
    if (ele) {
      return new Promise(resolve => {
        const image = new Image();
        image.src = ele;
        image.onload = () => {
          resolve(`
${ele}
`)
        };
        image.onerror = () => {
          resolve(`
${loadError}
`)
        };
      })
    } else {
      return Promise.resolve(`
${placeholder}
`)
    }
  })).then(arr => arr.join(''));
}
gen().then(html => {
  $("body").append(html)
})
const list = [
    "./img.png",//
    "//be-fe.github.io/static/images/iSlider-card/10.jpg",//
    "./load.gif",//
    "//be-fe.github.io/static/images/iSlider-card/12.jpg",//
    null,//
    "//be-fe.github.io/static/images/iSlider-card/17.jpg",//
];
const placeholder = '';
const loadError = '';
const gen = () =>
    list.map((ele) => new Promise(resolve => {
        function getsrc(src) {
            resolve(`
${src}
`)
        }
        if(ele){
            const image = new Image();
            image.src = ele;
            image.onload = () =>getsrc(ele)
            image.onerror = () => getsrc(loadError)
        }else {
            getsrc(placeholder)
        }
    }))
Promise.all(gen()).then(htmlArr =>  $("body").append(htmlArr.join('')));
< H2 > callback method < / H2 > 
const gen = () => {
    return new Promise((res, rej) => {
        let endSrc = placeholder;
        let html = '';
        list.forEach(ele) {
            if (ele) {
                const image = new Image();
                image.src = ele;
                image.onload = () => {
                    endSrc = ele;
                };
                image.onerror = () => {
                    endSrc = loadError;
                };
            }
            html += `
${endSrc}
`;
        });
        res(html);
    }
}
gen()
.then(html => {
    $("body").append(html);
})

and asnyc await , etc.

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