javascript - parseInt 有什么问题？

Question

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Answer 1

首先查阅 Array.prototype.map 的文档.关键是这一行:

callback is invoked with three arguments: the value of the element, the index of the element, and the Array object being traversed.

(强调我的)

然后检查 parseInt 的文档:

The parseInt function converts its first argument to a string, parses it, and returns an integer or NaN. If not NaN, the returned value will be the decimal integer representation of the first argument taken as a number in the specified radix (base). For example, a radix of 10 indicates to convert from a decimal number, 8 octal, 16 hexadecimal, and so on. For radices above 10, the letters of the alphabet indicate numerals greater than 9. For example, for hexadecimal numbers (base 16), A through F are used.

和:

If radix is undefined or 0, JavaScript assumes the following:

• If the input string begins with "0x" or "0X", radix is 16 (hexadecimal).

• If the input string begins with "0", radix is eight (octal). This feature is non-standard, and some implementations deliberately do not support it (instead using the radix 10). For this reason always specify a radix when using parseInt.

• If the input string begins with any other value, the radix is 10 (decimal).

所以第一个调用是:

parseInt('10',0, ['10','10',...]) // => 10 (because radix=0)

第二个是:

parseInt('10',1, ['10','10',...]) // => NaN because radix is 1

第三个:

parseInt('10',2, ['10','10',...]) // => 2 because 10 in binary is the number "2"

等等。