let str=true+11+null+9+undefined+"javascript"+false+null+9+[]+[" "]计算str
console.log(true+11) //12
console.log(12+null) //12
console.log(12+9) //21
console.log(21+undefined) //NaN
console.log(NaN+"javascript") //"NaNjavascript"
console.log("NaNjavascript" +false) //"NaNjavascriptfalse"
console.log("NaNjavascriptfalse"+null) //"NaNjavascriptfalsenull"
console.log("NaNjavascriptfalsenull"+9) //"NaNjavascriptfalsenull9"
console.log("NaNjavascriptfalsenull9"+[]) //"NaNjavascriptfalsenull9"
console.log("NaNjavascriptfalsenull9"+[" "] //"NaNjavascriptfalsenull9 "
Number()
console.log(Number("hello word")); //NaN
console.log(Number("")); //0
console.log(Number("000011")); //11
console.log(Number("true")); //NaN
console.log(Number(true)); //1
console.log(parseInt([3,2,3])); //3
console.log(parseFloat([1,2,3])); //1
数字,字符串计算
console.log(10 + "10"); //"1010"
console.log("10" + "10"); //"1010"
console.log(+"10"+ + "10"); //20
console.log((+"10") + (+"10")); // 20
console.log(-"10"+ 10); //0
js多个基本类型计算
