13 JavaScript Math对象

1 Math.ceil()

Math.ceil() 向上取整，'天花板函数'

var x = 1.234;
//天花板函数  表示大于等于 x，并且与它最接近的整数是2
var a = Math.ceil(x);
console.log(a); //2

2 Math.floor()

Math.floor 向下取整，'地板函数'

var x = 1.234;
// 小于等于 x，并且与它最接近的整数 1
var b = Math.floor(x);
console.log(b); //1

3 max()&min()

求两个数的最大值和最小值

//求 两个数的最大值 最小值
console.log(Math.max(2,5));//5
console.log(Math.min(2,5));//2

④ Math.random()

随机数 Math.random() 0<=random<1

var ran = Math.random();
console.log(ran); //[0,1)的随机数

5 属性介绍

console.log(Math.E); //2.718281828459045
console.log(Math.LN2); //0.6931471805599453
console.log(Math.LN10); //2.302585092994046
console.log(Math.LOG2E); //1.4426950408889634 
console.log(Math.LOG10E); //0.4342944819032518
console.log(Math.PI); //3.141592653589793
console.log(Math.SQRT2); //1.4142135623730951
console.log(Math.SQRT1_2); //0.7071067811865476

console.log(Math.abs(-12)); //-12的绝对值
console.log(Math.round(3.14)); //四舍五入
console.log(Math.pow(3,2)); //3的2次方等于9

6 Math练习

 //1.获取min到max之间的的整数(1~100)
function random(max,min) {
    return Math.floor(Math.random() * (max - min) + min);
}
console.log(random(100,1));

//2.获取随机颜色 rgb(0~255,0~255,0~255);
function randomColor() {
    var r = random(0,256),g = random(0,256),b = random(0,256);
    //模板字符串
    var result = `rgb(${r},${g},${b})`;
    return result;
}
console.log(randomColor());
//与html交互随机背景色
document.body.style.backgroundColor = randomColor();

//3.随机验证码 四位 数字+字母（大写）
function createCode() {
    //设置默认空的字符串
    var code = '';
    //设置长度
    var codeLength = 4;
    var randomCode= [0,1,2,3,4,5,6,7 ,8,9,'A','B' ,'C','D' ,'E','F',
        'G','H','I','J','K','L', 'M' ,'N','O' ,'P' ,'Q','R',
        'S','T','U','V','W','X','Y','Z'];
    for (var i = 0;i < codeLength;i++) {
        //随机范围0~36
        var index = random(0,36);
        code += randomCode[index];
    }
    return code;
}
console.log(createCode());
document.write(`<h1>${createCode()}</h1>`)