Javascript对象文字表示法，使用函数

Question

I'm creating an object using literal notation. Is it possible to have some of the properties use previously defined properties as their value?

For example:

    var test = {
        prop1: obj1, 
        prop2: obj2,
        prop3: (prop1!=null)?prop1:prop2
    };

Answer 1

If you are trying to do something like var x = { 'a': 1, 'b': xa } then it won't work. Since x is not finished being defined.

But you can do something like

var
    a = 12,
    b = 24,
    c = a + b; // 36

This is because each var definition is interpreted sequentially. Basically equivalent to

var a = 12;
var b = 24;
var c = a + b;

But with objects and arrays the entire definition is interpreted one time.

Answer 2

No and yes.

The following aren't possible:

var o = {
    a : 42,
    b : o.a //raises a TypeError, o is not defined
};

var o = {
    a : b : 42 //raises a SyntaxError, unexpected :
};

The following, however, are:

//referencing a pre-existing variable is obviously possible
var ans = 42;
var o = {
    a : ans,
    b : ans
};

var o = {
    a : 42
};
//after the variable has been declared, you can access it as usual
o.b = o.a;

If you feel limited by the value being a single statement, you can always use an anonymous function:

var o = {
    a : (function () {
        doStuff();
        return otherStuff();
    }())
};

Answer 3

to keep your example:

var test = {
  prop1: obj1,
  prop2: obj2,
  prop3: (function () {
    return (test.prop1!=null)?test.prop1:test.prop2;
  })()
};