javascript

CHAPTER 3 ■ OPERATORS
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mincedLemonZest: [2, "tsp"],
seaSalt: [1/4, "tsp"],
soda: [1, "tsp"],
tartar: [1, "tsp"],
pourableVanillaYogurt: [1, "cup"],
egg: [1],
wildBlueberries: [1 + 1/4, "cup"]
};
dough.pourableVanillaYogurt[0] += "1";
dough.pourableVanillaYogurt[0];
// "11"
Figure 3–3. += only does concatenation if its right operand is not a number.
Remember that every JavaScript value can be converted to a boolean or string, but not to a number.
Not one you can do math with anyway. Most non-numbers convert to the “not a number” literal NaN.
Moreover, the return value of any math operation containing a NaN operand will always be NaN.
Insofar as JavaScript returns NaN whenever a value cannot be converted to a number, +=, -=, *=, and
/= may overwrite a variable, member, element, or parameter with NaN. To illustrate the point, try the
following sample, verifying your work with Figure 3–4. Insofar as we forgot to refine our query with the
[] operator, JavaScript multiplies the array [1 + 1/4, “cup”] by 3. Therefore, [1 + 1/4, “cup”] is converted
to the number NaN and multiplied by 3. So, the array in dough.wildBlueberries is overwritten with the
return value of NaN * 3, which of course is NaN.
var dough = {
pastryFlour: [1 + 3/4, "cup"],
almondFlour: [1/3, "cup"],
saigonCinnamon: [1, "tsp"],
mincedLemonZest: [2, "tsp"],
seaSalt: [1/4, "tsp"],
soda: [1, "tsp"],
tartar: [1, "tsp"],
pourableVanillaYogurt: [1, "cup"],
egg: [1],
wildBlueberries: [1 + 1/4, "cup"]
};