js//输入斐波那契数列的项数num,求前num项的和 //示例：输入5，输出结果“斐波那契数列的前5项之和为12”

let num = parseInt(prompt("请输入斐波那契数列的项数："));
let sum = 0;
let a = 1, b = 1;
for (let i = 1; i <= num; i++) {
sum += a;
let temp = a + b;
a = b;
b = temp;
}
console.log("斐波那契数列的前" + num + "项之和为" + sum);