calling a functions value [duplicate]

问题

This question already has answers here:

Closed 7 years ago.

Possible Duplicate:
Function triggering early

I have whipped up this code, but why on earth would it be alerting me that its undefined even though I have never even got a chance to click on and select a date from the UI date picker when I call the function test()?

Doesn't seem to make sense with me?

var sdate

function test() {
    alert(select_date())
}

function select_date() {
    $('#dd').dialog({
        autoOpen: true,
        modal: true,
        overlay: {
            opacity: 0.5,
            background: 'black'
        },
        title: "title",
        height: 265,
        width: 235,
        draggable: false,
        resizable: false
    }); //end of dialog

    $('#d1').datepicker({
        onSelect: function() {
            sdate = $(this).val();
            $("#dd").dialog("close");
        }
    });
    return sdate
}​

回答1:

onSelect is an event callback, you are trying to return a value before it knows what to do. it's not going to be possible to have your test() return the value, because it comes later.

you should do your alert or whatever logic from within the event callback:

$('#d1').datepicker({
    onSelect: function() {
        sdate = $(this).val();
        $("#dd").dialog("close");
        alert(sdate);
        // or your own function
        someOtherTest(sdate);
    }
});

-

function someOtherTest(date) {
    alert(date);
}

来源：https://stackoverflow.com/questions/12202188/calling-a-functions-value