let res = 3 % -10
console.log(res) // 3
取余数运算中,如果右侧数值小于左侧,则结果为左测数值
let res = 2 * 2 * undefined
console.log(res) // NaN
undefined在转化为数值类型时是NaN
let a = 5, b, c;
b = a = c
console.log(a, b, c) //undefined undefined undefined
赋值运算符遵行右结合性,从右向左开始赋值