javascript

CHAPTER 2 ■ TYPE CONVERSION
Note too that, if either operand to a math operator like * or - is NaN, the return value will be NaN, too.
Therefore, as Figure 2–22 displays, you can do math with null but not with undefined.
var nothing, zilch = null;
nothing * 4;
// NaN
zilch * 4;
// 0
Figure 2–22. JavaScript can do math with null but not with undefined.
Converting strings to numbers is fairly straightforward. Number-like strings such as "4" or "3.33"
convert to an equivalent number (4 and 3.33). The "" empty string converts to 0. Everything else
converts to NaN. Let’s try converting a few strings to a number in Firebug, verifying our work with Figure
2–23:
Number("4");
// 4
Number("");
// 0
Number("Mr. Incredible");
// NaN
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