美团到店一面
1、看输出
setTimeout(() => {
console.log(2)
Promise.resolve().then(() => {
console.log(3)
})
})
new Promise((resolve) => {
console.log(4)
setTimeout(() => {
console.log(5)
resolve();
}, 2);
}).then(res => {
console.log(res)
});2、数组扁平化，能控制扁平化层级
array.flat(arr, dep)
[1, [2, [ 3, 4]]]
[1, 2, [3, 4]]
