【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