js中三元运算符 ?

语法：条件？表达式1：表达式2

var even = (n % 2 === 0 ) ? true :false

上面代码的含义是 如果n可以被2整除，则even等于true，否则等于false

var even;
if(n % 2 === 0){
    even = true;
} else {
    even = false;
}


var myVar;
console.log(
  myVar ?
  'myVar has a value' :
  'myVar does not have a value'
)
// myVar does not have a value

var msg = '数字' + n + '是' + (n % 2 === 0 ? '偶数' : '奇数');