Javascript"预设"变量？

Question

我正在尝试声明一个变量,其值是另一个当时未设置的变量.

var add = 1 + three;
var three = 3;
document.getElementById('thediv').innerHTML = add;
//results in "NaN"

http://jsfiddle.net/seSMx/1/

有没有办法使用Jquery/Javascript来做到这一点？

Answer 1

你可以把添加到一个函数,

http://jsfiddle.net/seSMx/3/

function add() {
   return 1 + (three || 0);
}

var three = 3;
document.getElementById('thediv').innerHTML = add();

虽然,在我看来这很难遵循.我会更进一步,并进行three争论add

function add(three) {
   return 1 + (three || 0);
}

document.getElementById('thediv').innerHTML = add(3);

Answer 2

这是你要的吗？

var add = "1 + three";
var three = 3;
document.getElementById('thediv').innerHTML = eval(add);