JavaScript学习笔记

Boolean运算符

number => boolean 0 和NaN为 false , 其余为true;

string =>boolean ""为false 其余为true;

null => boolean false;

undefined => boolean false;

Object => boolean true;

数学运算符

var a="1"+1; a ="11";

var a= "1"-1;a=0;

关系运算符

“2”>1; 会把“2”转成number 在比较

“a”>"b" 字符串比较 实际上是比较字符串的asc码

等性运算符

null==undefined => true;

"NaN"==NaN =>false;

5==NaN => false;

NaN ==NaN => false;

NaN !=NaN => true;

false==0 =>true;

true==1 =>true;

true==2 =>false;

undefined ==0 =>false;

null==0 =>false;

"5"==5 =>true;

=== :全等于符号 比较时包括类型本身

1===true => false