If the value isn't a number (say it's number (xyz), for example), the function returns the string NaN (not a number).

如果值不是数字(譬如，假设它是number (xyz))，则函数返回字符串NaN(表示不是数字)。

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When you preview the form to check the calculations, you see that the input fields for Subtotal and Total Price contain the letters NaN, which stand for Not a Number.

当预览表单以检查计算时，可以看到 Subtotal 和 Total Price 的输入字段包含字母 NaN，这表示这个字段不是数字。

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Many routines designed to read floats may allow values such as "NaN" (not a number).

许多设计用来读取浮点数的例程可能会允许“NaN”(非数字)这样的值。

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