-
数据类型
基本数据类型：Undefined、Null、Boolean、Number、String
引用数据类型：Object
typeof
检测null时会返回object，
因为null类型的机器码全是0，
而typeof检测到后三位全是0的时候，会返回object
检测到object类型之后，会再次调用内部的一个[[call]]函数，如果有则返回function，否则返回object
let str = "asdf";
typeof返回string，栈类型存储
let str = new String("asdf")
typeof 返回object，堆类型存储
instanceof
通过原型链来检测，返回boolean值，true false
A instanceof B
A是否是B的实例对象
查看全部 -
浮动数相加不准确问题在于计算机会把浮点数转成二进制 超过计算机存储长度之后 会舍掉 导致转换回来之后数字不精确
// 省略小数点2位之后数字
console.log(parseFloat(0.1+0.2).toFixed(2));
//转成整数类型
function add(m1,m2){
var m=Math.pow(10,2);
return (m1*m+m2*m)/m
}
console.log(add(0.1,0.2));
查看全部 -
NaN undefined 0 null "" 会转换成false
其余都是true
查看全部 -
基本数据(简单数据类型 值类型)类型存放在栈中,引用数据类型(复杂数据类型 对象类型)的数据存放在堆中,但是引用数据类型的地址存放在栈中
查看全部 -
typeof检测引用类型function的时候 会返回function 而不是object,这是在设计js的时候检测引用类型,会检查是否包含[ [call] ]方法,包含的会返回function 不包含的返回object
查看全部 -
typeof检查null的时候 返回的数据类型是根据机器码的后三位而决定的 当检测到null的时候返回000 =>object
查看全部 -
function instanceof(A,B){ let p=A while(p){ if(p===B.prototype){ return true } p=p._proto_ } return false }typeof 返回的是数据的类型，instanceof返回的是布尔值
查看全部 -
遍历赋值 -> 简单循环赋值是浅拷贝，递归循环判断类型赋值：是深拷贝
Object.create() -> 简单循环赋值是浅拷贝，递归循环判断类型赋值：是深拷贝
JSON.parse()和JSON.stringify() ->深拷贝
深浅拷贝：假设B复制了A,当修改A时，看B是否发生变化，B变了，说明时浅拷贝；B没变，就是深拷贝
查看全部 -
老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好
查看全部 -
老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好
查看全部 -
老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好
查看全部 -
老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好
查看全部 -
老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好
查看全部 -
老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好
查看全部 -
老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好老师讲得好
查看全部
举报