1
2
3
null > 0   // null 尝试转型为number，则为0，所以结果为 false
null >= 0  // null 尝试转为number，则为0，结果为 true
null == 0  // null在设计上，在此处不尝试转型，所以结果为 false
  • 内部相等性运算算法

11.9.3 The Abstract Equality Comparison Algorithm
The comparison x == y, where x and y are values, produces true or false. Such a comparison is performed as follows:

  1. If Type(x) is different from Type(y), Go to step 14.
  2. If Type(x) is Undefined, return true.
  3. If Type(x) is Null, return true.
  4. If Type(x) is not Number, go to step 11.
  5. If x is NaN, return false.
  6. If y is NaN, return false.
  7. If x is the same number value as y, return true.
  8. If x is +0 and y is -0, return true.
  9. If x is -0 and y is +0, return true.
  10. Return false.
  11. If Type(x) is String, then return true if x and y are exactly the same sequence of characters (same length and same characters in corresponding positions). Otherwise, return false.
  12. If Type(x) is Boolean, return true if x and y are both true or both false. Otherwise, return false.
  13. Return true if x and y refer to the same object or if they refer to objects joined to each other (see 13.1.2). Otherwise, return false.
  14. If x is null and y is undefined, return true.
  15. If x is undefined and y is null, return true.
  16. If Type(x) is Number and Type(y) is String, return the result of the comparison x == ToNumber(y).
  17. If Type(x) is String and Type(y) is Number, return the result of the comparison ToNumber(x)== y.
  18. If Type(x) is Boolean, return the result of the comparison ToNumber(x)== y.
  19. If Type(y) is Boolean, return the result of the comparison x == ToNumber(y).
  20. If Type(x) is either String or Number and Type(y) is Object, return the result of the comparison x == ToPrimitive(y).
  21. If Type(x) is Object and Type(y) is either String or Number, return the result of the comparison ToPrimitive(x)== y.
  22. Return false.
  • 内部关系运算算法

11.8.5 The Abstract Relational Comparison Algorithm
The comparison x < y, where x and y are values, produces true, false, or undefined (which indicates that at least one operand is NaN). Such a comparison is performed as follows:

  1. Call ToPrimitive(x, hint Number).
  2. Call ToPrimitive(y, hint Number).
  3. If Type(Result(1)) is String and Type(Result(2)) is String, go to step 16. (Note that this step differs from step 7 in the algorithm for the addition operator **+ * in using *and instead of or.)
  4. Call ToNumber(Result(1)).
  5. Call ToNumber(Result(2)).
  6. If Result(4) is NaN, return undefined.
  7. If Result(5) is NaN, return undefined.
  8. If Result(4) and Result(5) are the same number value, return false.
  9. If Result(4) is +0 and Result(5) is -0, return false.
  10. If Result(4) is -0 and Result(5) is +0, return false.
  11. If Result(4) is +∞, return false.
  12. If Result(5) is +∞, return true.
  13. If Result(5) is -∞, return false.
  14. If Result(4) is -∞, return true.
  15. If the mathematical value of Result(4) is less than the mathematical value of Result(5) — note that these mathematical values are both finite and not both zero — return true. Otherwise, return false.
  16. If Result(2) is a prefix of Result(1), return false. (A string value p is a prefix of string value q if q can be the result of concatenating p and some other stringr. Note that any string is a prefix of itself, because r may be the empty string.)
  17. If Result(1) is a prefix of Result(2), return true.
  18. Let k be the smallest nonnegative integer such that the character at position k within Result(1) is different from the character at position k within Result(2). (There must be such a k, for neither string is a prefix of the other.)
  19. Let m be the integer that is the code point value for the character at position k within Result(1).
  20. Let n be the integer that is the code point value for the character at position k within Result(2).
  21. If m < n, return true. Otherwise, return false.
  • “>” 运算符

The Greater-than Operator ( > )
The production RelationalExpression :
RelationalExpression > ShiftExpression is evaluated as follows:

  1. Evaluate RelationalExpression.
  2. Call GetValue(Result(1)).
  3. Evaluate ShiftExpression.
  4. Call GetValue(Result(3)).
  5. Perform the comparison Result(4) < Result(2).
  6. If Result(5) is undefined, return false. Otherwise, return Result(5).
  • ”>=” 运算符

The Greater-than-or-equal Operator ( >= )
The production RelationalExpression :
RelationalExpression >= ShiftExpression is evaluated as follows:

  1. Evaluate RelationalExpression.
  2. Call GetValue(Result(1)).
  3. Evaluate ShiftExpression.
  4. Call GetValue(Result(3)).
  5. Perform the comparison Result(2) < Result(4). (see 11.8.5).
  6. If Result(5) is true or undefined, return false. Otherwise, return true.
  • “==” 运算符

The Equals Operator ( == )
The production EqualityExpression :
EqualityExpression == RelationalExpression is evaluated as
follows:

  1. Evaluate EqualityExpression.
  2. Call GetValue(Result(1)).
  3. Evaluate RelationalExpression.
  4. Call GetValue(Result(3)).
  5. Perform the comparison Result(4) == Result(2). (see 11.9.3).
  6. Return Result(5).

根据以上ES3的实现，得出以下结论：

  1. 关系运算符 和 相等运算符 并不是一个类别的.
  2. 关系运算符,在设计上,总是需要运算元尝试转为一个number . 而相等运算符在设计上,则没有这方面的考虑.
  3. 最重要的一点, 不要把 拿 a > b , a == b 的结果 想当然的去和 a >= b 建立联系. 正确的符合最初设计思想的关系是 a > b 与 a >= b是一组 . a == b 和其他相等运算符才是一组. 比如 a === b , a != b, a !== b .
1
2
3
null > 0   // null 尝试转型为number，则为0，所以结果为 false
null >= 0  // null 尝试转为number，则为0，结果为 true
null == 0  // null在设计上，在此处不尝试转型，所以结果为 false

ps:这设计真是令人无语