计算一个数的绝对值

function abs(x) {if (x >= 0) {return x;} else {return -x;}
}
console.log(abs(10) === abs(-10)); //=>true

计算数组元素之和

let arr = [1, 3, 5];function sum(array) {let sum = 0;for (let x of array) {	//循环数组把每个元素赋给xsum += x;}return sum;
}
console.log(sum(arr));

计算阶乘（1）

function factorial(n) {let product = 1;	//乘积初始化为1while (n > 1) {product *= n;n--;}return product;
}
console.log(factorial(4));	//=> 24:1*4*3*2

计算阶乘（2）

function factorial2(n) {let product = 1;for (i = 2; i <= n; i++) {product *= i;}return product;
}
console.log(factorial2(4));	//=>24:1*2*3*4