The big pit inside the "+" sign in JavaScript

1 + number inside the big pit;2 1, String + any number is stitching3 var a = 3;4 var b = "4";5 alert (a+b);//346 7 2, undefined+ any string is stitching8 var A;9 var b = "Zhang San";Ten alert (a+b);//a Zhang San One  A 3, false+ any number false to the implicit type conversion to 0 - var bool = false; - var num1 = 3; the alert (BOOL+NUM1);//3 -              - 4, true+ any number true for implicit type conversion to 0 - var bool = true; + var num1 = 3; - alert (BOOL+NUM1);//4 +              A 5, null+ any string; splicing at var str = null; - var num1 = "Zhang San"; - alert (STR+NUM1);//null Zhang San -         

The big pit inside the "+" sign in JavaScript