为什么await在forEach中无效

错误写法

  function api(i) {
        return new Promise((resolve, reject) => {
            setTimeout(() => {
                const n = Math.random();
                if (n > 0.5) {
                    resolve(n);
                } else {
                    resolve(-n)
                }
            }, 1000 * 1);
        });
    }
    const list = [1, 2, 3, 4, 5];
    async function fn() {
        // 数组forEach遍历方法 await无效
        list.forEach(async (el, index) => {
            const n = await api(index);
            console.log(n, index);
        });
    };
    fn();

正确写法

function api(i) {
        return new Promise((resolve, reject) => {
            setTimeout(() => {
                const n = Math.random();
                if (n > 0.5) {
                    resolve(n);
                } else {
                    resolve(-n)
                }
            }, 1000 * 1);
        });
    }
    const list = [1, 2, 3, 4, 5];

    async function fn() {
        for (let i = 0; i < list.length; i++) {
            const n = await api(i);
            console.log('for--------', n, i);
        }
    };
    fn();

await要写在async函数里面，await只是语法糖，使异步变成同步，便于书写和阅读。await 等待异步的promise函数执行完成resolve或者reject,抛异常使用try catch。forEach使用await无效，改用for循环