JavaScript: The Definitive Guide, Fourth Edition

String Operators

As we’ve discussed in the previous sections, there are several operators that have special effects when their operands are strings.

The + operator concatenates two string operands. That is, it creates a new string that consists of the first string followed by the second. For example, the following expression evaluates to the string “hello there”:

"hello" + " " + "there"

And the following lines produce the string “22”:

a = "2"; b = "2";
c = a + b;

The < , <=, >, and >= operators compare two strings to determine what order they fall in. The comparison uses alphabetical order. As noted above, however, this alphabetical order is based on the Unicode character encoding used by JavaScript. In this encoding, all capital letters in the Latin alphabet come before (are less than) all lowercase letters, which can cause unexpected results.

The == and != operators work on strings, but, as we’ve seen, these operators work for all data types, and they do not have any special behavior when used with strings.

The + operator is a special one -- it gives priority to string operands over numeric operands. As noted earlier, if either operand to + is a string (or an object), the other operand is converted to a string (or both operands are converted to strings) and concatenated, rather than added. On the other hand, the comparison operators perform string comparison only if both operands are strings. If only one operand is a string, JavaScript attempts to convert ...