javascript - JavaScript中的（内置）方式来检查字符串是否为有效数字((Built-in) way in JavaScript to check if a string is a valid number)

Question

我希望在与旧的VB6 IsNumeric()函数相同的概念空间中有东西吗？

  ask by Electrons_Ahoy translate from so

Answer 1

To check if a variable (including a string) is a number, check if it is not a number:(要检查变量（包括字符串）是否是数字，请检查它是否不是数字：)

This works regardless of whether the variable content is a string or number.

(无论变量内容是字符串还是数字，这都有效。)

isNaN(num)         // returns true if the variable does NOT contain a valid number

Examples(例子)

isNaN(123)         // false
isNaN('123')       // false
isNaN('1e10000')   // false (This translates to Infinity, which is a number)
isNaN('foo')       // true
isNaN('10px')      // true

Of course, you can negate this if you need to.

(当然，您可以根据需要对此进行否定。)

For example, to implement the IsNumeric example you gave:

(例如，要实现您提供的IsNumeric示例：)

function isNumeric(num){
  return !isNaN(num)
}

To convert a string containing a number into a number:(要将包含数字的字符串转换为数字：)

Only works if the string only contains numeric characters, else it returns NaN .

(仅当字符串仅包含数字字符时才有效，否则返回NaN 。)

+num               // returns the numeric value of the string, or NaN 
                   // if the string isn't purely numeric characters

Examples(例子)

+'12'              // 12
+'12.'             // 12
+'12..'            // Nan
+'.12'             // 0.12
+'..12'            // Nan
+'foo'             // NaN
+'12px'            // NaN

To convert a string loosely to a number(将字符串宽松地转换为数字)

Useful for converting '12px' to 12, for example:

(有助于将“ 12px”转换为12，例如：)

parseInt(num)      // extracts a numeric value from the 
                   // start of the string, or NaN.

Examples(例子)

parseInt('12')     // 12
parseInt('aaa')    // NaN
parseInt('12px')   // 12
parseInt('foo2')   // NaN      These last two may be different
parseInt('12a5')   // 12       from what you expected to see. 

Floats(浮点数)

Bear in mind that, unlike +num , parseInt (as the name suggests) will convert a float into an integer by chopping off everything following the decimal point (if you want to use parseInt() because of this behaviour, you're probably better off using another method instead ):

(请记住，与+num不同， parseInt （顾名思义）将通过截取小数点后的所有内容将浮点数转换为整数（如果由于这种行为而想使用parseInt() ，则可能更好）使用另一种方法代替 ）：)

+'12.345'          // 12.345
parseInt(12.345)   // 12
parseInt('12.345') // 12

Empty strings(空字符串)

Empty strings may be a little counter-intuitive.

(空字符串可能有点违反直觉。)

+num converts empty strings to zero, and isNaN() assumes the same:

(+num将空字符串转换为零，并且isNaN()假定相同：)

+''                // 0
isNaN('')          // false

But parseInt() does not agree:

(但是parseInt()不同意：)

parseInt('')       // NaN