Automatic type conversion for numbers and strings

When you use -, *, or / on any inputs, the output will be of type number (possibly NaN). Notice that null and false are assigned the numerical value 0 and true is assigned the numerical value 1, but that calculating with undefined results in NaN. Similarly, notice how "5" is interpreted as the integer 5 and "3.4" as the floating point number 3.4, but a calculation using "dog" results in NaN.

Be very careful of +, which has meanings for both numbers and strings. If at least one of the inputs is a string, the output will be a string. Notice that this also applies to the shorthand +=; if you use n += "string" for a number n, n is converted into a string.