数据类型转换

字符串转换数字
var a = ‘1‘;
console.log(+a);
console.log(a++);
console.log(-a+3);
console.log(parseInt(a));
console.log(parseFloat(a));
console.log(Number(a));

数字转换字符串
var a = 1;
a+‘‘
String(a);
a.toFixed();
a.toLocaleString();
a.toPrecision();
a.toString();




数组转字符串
var arr = [1,2,3];
arr.toString();
arr+"";

数组转数字，只能有一位，否则NaN
var arr = [1];
++arr;
+arr;
arr--;
arr-0
arr.toString()-0

console.log(1 +  "2" + "2"); //‘122‘
console.log(1 +  +"2" + "2"); //‘32‘
console.log(1 +  -"1" + "2"); //‘02‘
console.log(+"1" +  "1" + "2"); //‘112‘
console.log( "A" - "B" + "2"); //‘NaN2‘
console.log( "A" - "B" + 2); //‘NaN‘