【学习笔记】JS Math&Json&异常处理机制

Math下的属性&方法

1. E：2.718281828459045
2. LN2:0.6931471805599453
3. LN10:2.302585092994046
4. LOG2E:1.4426950408889634
5. LOG10E:0.4342944819032518
6. PI:3.141592653589793
7. SQRT1_2:0.7071067811865476
8. SQRT2:1.4142135623730951

var vva = 1.2345678;console.log(vva.toFixed(3));//进位，小数点后3位console.log(vva.toPrecision(3));//进位console.log(vva.toExponential(5));//科学计数法console.log(vva.toString());

var uu1 = {    uu11: 112,    uu12: [12, 324, 34],    uu13: {oo: 1,o1:2},    uu14: function fcc() {        var b = {e:123,r:234};        return b;    },    uu15: {oo3: 34, oo1:23, oo2:[2,3,[23,34,34],34]}};console.log( 'uu11' in uu1); //判断的是下标var ii = 1;console.log(ii);eval('ii = 2'); //将字符串变为程序语句console.log(ii);

console.log(JSON.parse('{"uu11":112,"uu12":[12,324,34],"uu13":{"oo":1,"o1":2},"uu15":{"oo3":34,"oo1":23,"oo2":[2,3,[23,34,34],34]}}'));console.log(JSON.stringify(uu1));

捕获可能出现的错误并且输出，不影响下方程序的进行

try{    var a88 = 0;    var b88 = 'df ';    var c88 = b88 / a88;    console.log(document.getElementById('body').innerHTML);}catch (e){    console.log(e)}

function Test() {    console.log(this instanceof Test);    if(typeof this === 'undefined'){  //typeof 任意一个变量 出来的都是字符串        throw TypeError("出错了,不能直接调用构造函数");    }    if(!(this instanceof Test)){  //两种方式        throw Error("出错！");    }}var test1 = new Test();//创建实例对象Test(); //不是Test的实例对象