JavaScript中的逻辑运算符评估

Question

Can you explain how works the Comparison Operators in JS:

 "a" > "A" // => why true?
  null == undefined; // and here as well?

and some others

   null >  0;
   null >= 0;

Answer 1

Strings are compared by their character codes, ie. their positions in the Unicode table.
A is 65, a is 97. Therefore "a" > "A" .

== is a loose comparison. null == undefined is a special case, since the abstract equality comparison algorithm explicitly states that true should be returned when comparing these two values:

2. If x is null and y is undefined , return true .
3. If x is undefined and y is null , return true .

null > 0 is false, and null >= 0 is true because null , when converted to a number, is zero.