遍历的几种比较

var someArray = [9, 2, 5];
someArray.forEach((item, index,arr) => {
console.log(item); // 9, 2, 5
console.log(index); // 0, 1, 2
console.log(arr); // [9, 2, 5]
});

for of 也是一样的
for (let [index, value] of array.entries()) {
console.log(index); // 0, 1, 2
console.log(item); // 9, 2, 5
}

for (const {item, index} of someArray.map((item, index) => ({ item, index }))) {
console.log(item); // 9, 2, 5
console.log(index); // 0, 1, 2
}