当字符串中为整数
let str = '123'
console.log(Number(str)) // output: 123
console.log(Number.parseInt(str)) // output: 123
console.log(Number.parseFloat(str)) // output: 123
当字符串中为浮点数
let str2 = '123.01'
console.log(Number(str2)) // output: 123.01
console.log(Number.parseInt(str2)) // output: 123
console.log(Number.parseFloat(str2)) // output: 123.01
当字符串结尾为字母
let str3 = '123.01a'
console.log(Number(str3)) // output: NaN
console.log(Number.parseInt(str3)) // output: 123
console.log(Number.parseFloat(str3)) // output: 123.01
当字符串开头和结尾未字母
let str4 = 'abc123.01a'
console.log(Number(str4)) // output: NaN
console.log(Number.parseInt(str4)) // output: NaN
console.log(Number.parseFloat(str4)) // output: NaN
当字符串中间包含字母
let str5 = '12bc3.01'
console.log(Number(str5)) // output: NaN
console.log(Number.parseInt(str5)) // output: 12
console.log(Number.parseFloat(str5)) // output: 12
