parseFloat直接可以转换,帮助文件里面有说啊
Returns a floating-point number converted from a string.
parseFloat(numString)
The required numString argument is a string that contains a floating-point number.
Remarks
The parseFloat method returns a numerical value equal to the number contained in numString. If no prefix of numString can be successfully parsed into a floating-point number, NaN (not a number) is returned.
parseFloat("abc") // Returns NaN.
parseFloat("1.2abc") // Returns 1.2.
You can test for NaN using the isNaN method.