如何使用 async/await 实现 Promise.all 的效果

const all = (list) => {
    const res = new Promise((resolve, reject) => {
        let length = list && list.length
        let count = 0
        let result = []
        if(!list || list.length === 0) {
            resolve(result)
        }
        list.forEach(async (item, index) => {
            try {
                const res = await item
                result[index] = res
                count ++
                if(count === length) {
                    resolve(result)
                }
            } catch(err) {
                reject(err)
            }
        });
    })
    return res
}