将字符串转换成数字

1. parseInt（）
   字符串第一个字符是数字，直到碰到小数点或者其他字符

var a = parseInt('10.36aa')//10
var a=parseInt('.10.36aa')//NaN

1. parseFloat()
   如果第一个字符是小数点，则以0.开头直到遇到第二个小数点或者其他字符

var a = parseFloat('.36.33aa')//0.36
var a = parseFloat('10.36.33aa')//10.36
var a = parseFloat('a.36.33aa')//NaN

1. +

var a = +'a.36.33aa'//NaN
var a = +'.36.33aa'//NaN
var a = +'0.36.33'//NaN
var a = +'0.36'//0.36

1. Number()
   强制转换

var a = Number('.36')//0.36
var a = +'a.36.33aa'//NaN
var a = +'.36.33aa'//NaN
var a = +'0.36.33'//NaN