Why is one string greater than the other when comparing strings in JavaScript?

Question

I see this code from a book:

var a = \"one\";
var b = \"four\";
a>b; // will return true

but it doesn\'t mention why \"one\" is bigger t

Answer 1

In the 11th edition of the ECMAScript Language Specification the "Abstract Relational Comparison" clause defines how to compute x < y. When the expression is reverted (i.e. x > y) we should compute the result of y < x instead.

So to solve "one" > "four" we must solve "four" < "one" instead.

The same clause says this:

The comparison of Strings uses a simple lexicographic ordering on sequences of code unit values.

And this if both operands are strings:

3. If Type(px) is String and Type(py) is String, then
   • If IsStringPrefix(py, px) is true, return false.
   • If IsStringPrefix(px, py) is true, return true.
   • Let k be the smallest nonnegative integer such that the code unit at index k within px is different from the code unit at index k within py. (There must be such a k, for neither String is a prefix of the other.)
   • Let m be the integer that is the numeric value of the code unit at index k within px.
   • Let n be the integer that is the numeric value of the code unit at index k within py.
   • If m < n, return true. Otherwise, return false.

(We can safely ignore the first two points for this example)

So let's see the code units for "four":

[..."four"].map(c => c.charCodeAt(0));
//=> [102, 111, 117, 114]

And for "one":

[..."one"].map(c => c.charCodeAt(0));
//=> [111, 110, 101]

So now we must find a value for k (starting at 0) where both m[k] and n[k] are different:

|   | 0   | 1   | 2   | 3   |
|---|-----|-----|-----|-----|
| m | 102 | 111 | 117 | 114 |
| n | 111 | 110 | 101 |     |

We can see that at 0 both m[0] and n[0] are different.

Since m[0] < n[0] is true then "four" < "one" is true and thus "one" > "four" is true.

---

What does "☂︎" < "☀︎" return?

[..."☂︎"].map(c => c.charCodeAt(0))
//=> [9730, 65038]
[..."☀︎"].map(c => c.charCodeAt(0))
//=> [9728, 65038]

|   | 0    | 1     |
|---|------|-------|
| m | 9730 | 65038 |
| n | 9728 | 65038 |

Since 9730 < 9728 is false then "☂︎" < "☀︎" is false which is nice because rain is not better than sun (obviously ;).