JavaScript错误，未定义，不是对象

Question

I am new in JavaScript, And I am trying to map my controller's buttons and leds for mixxx application. Is that an object, an array? var is missing.

BehringerCMDMM1.leds = [
    // Master
    { "shiftButton" : 0x12 },
    // Deck 1
    {  "sync" : 0x30  },
    // Deck 2
    {  "sync" : 0x33  }
];

I have an error here,

BehringerCMDMM1.shiftButton = function (channel, control, value, status, group) {
// Note that there is no 'if (value)' here so this executes both when the shift button is pressed and when it is released.
// Therefore, BehringerCMDMM1.shift will only be true while the shift button is held down
var deck = BehringerCMDMM1.groupToDeck(group);
BehringerCMDMM1.shift = !BehringerCMDMM1.shift // '!' inverts the value of a boolean (true/false) variable
BehringerCMDMM1.setLED(BehringerCMDMM1.leds[deck]["shiftButton"], BehringerCMDMM1.shift);

}

about "shiftButton" as undefined.

also I have this function

BehringerCMDMM1.setLED = function(value, status) {

status = status ? 0x7F : 0x00;
midi.sendShortMsg(0x94, value, status);

}

This is from a javascript file I found on the internet created for a different controller. So, I am trying things to understand how can I configure mine.

Answer 1

BehringerCMDMM1.leds is an array of objects. Within that array, the element at index 0 is an object that has a shiftButton property. Thus, the only way to get the 0x12 value in your example is to do this:

BehringerCMDMM1.leds[0]['shiftButton']

So when this code executes...

var deck = BehringerCMDMM1.groupToDeck(group);

...the value of deck is probably something other than 0, and you're accessing one of the sync objects in the BehringerCMDMM1.leds array. For example, if the value of deck was 1, then this...

BehringerCMDMM1.leds[deck]['shiftButton']

...will be undefined because you're effectively doing this:

BehringerCMDMM1.leds[1]['shiftButton']

Answer 2

Ok,

I am new in JavaScript, And I am trying to map my controller's buttons and leds for mixxx application. Is that an object, an array?

You have a array of objects.

var is missing.

You should test what is inside yout deck variable. Try this:

console.log(deck);
if (deck in BehringerCMDMM1.leds) {
    BehringerCMDMM1.setLED(BehringerCMDMM1.leds[deck]["shiftButton"], BehringerCMDMM1.shift);
} else {
    console.log("Index: "+deck+" doesn't exist");
}