Part1.第一遍学习遇到的函数什么的。。
**prompt** : get a input eg. prompt("What is Ubuntu? ");
**console.log**: like print eg. console(something);
**substring(x, y)**: print part string eg."Hello".substring(0, 3);
**Math.random()**: make a random number between 0 and 1
**Math.floor()**: return no more than the Integer
**iSNaN**: check is a number or not, yes is false, no is true