JS variable is equal to 0, etc. '

var a = 0;

if(a==""){

a = 2;

}

The final result of this line of code ,a by 2; because ：a==0==""==false;

stay js in 0、false、"" Is the default value of equality ;

Such as int The default value is 0,bool The default value is false, The default value of the string is "" namely ：

0==false==""

1==true="1"

As a weakly typed language, it must be compatible with the definitions of various types , Generally, these three types are used ;

So to solve this problem , You can judge first isNaN, In judging typeOf type , Do the conversion again parseInt... Mode switching ;