gistfile1.js

var b = require('bonescript');
b.pinMode("P8_12", b.INPUT);
setInterval(check,100);

function check() {
  b.digitalRead(pin, checkButton);
}

function checkButton(x) {
  if (x.value == 1) {
    console.log("High");
  }
  else {
    console.log("Low");
  }
}

/usr/local/lib/node_modules/bonescript/my.js:57
            if(slot[0]) {
                   ^
TypeError: Cannot read property '0' of null
    at Object.exports.load_dt (/usr/local/lib/node_modules/bonescript/my.js:57:20)
    at Object.exports.create_dt (/usr/local/lib/node_modules/bonescript/my.js:123:33)
    at Object.exports.setPinMode (/usr/local/lib/node_modules/bonescript/hw_capemgr.js:83:12)
    at Object.f.pinMode (/usr/local/lib/node_modules/bonescript/index.js:160:15)
    at Object.<anonymous> (/var/lib/cloud9/bbb_read_button.js:2:3)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Module.runMain [as _onTimeout] (module.js:497:10)

[Process stopped]

[  438.572710] bone-capemgr bone_capemgr.9: part_number 'GPIO_P8_12_0x37', version 'N/A'
[  438.572796] bone-capemgr bone_capemgr.9: slot #7: generic override
[  438.572816] bone-capemgr bone_capemgr.9: bone: Using override eeprom data at slot 7
[  438.572836] bone-capemgr bone_capemgr.9: slot #7: 'Override Board Name,00A0,Override Manuf,GPIO_P8_12_0x37'
[  438.572944] bone-capemgr bone_capemgr.9: slot #7: Requesting part number/version based 'GPIO_P8_12_0x37-00A0.dtbo
[  438.572965] bone-capemgr bone_capemgr.9: slot #7: Requesting firmware 'GPIO_P8_12_0x37-00A0.dtbo' for board-name 'Override Board Name', version '00A0'
[  438.574766] bone-capemgr bone_capemgr.9: slot #7: dtbo 'GPIO_P8_12_0x37-00A0.dtbo' loaded; converting to live tree
[  438.575069] bone-capemgr bone_capemgr.9: slot #7: #2 overlays
[  438.581461] bone-capemgr bone_capemgr.9: slot #7: Applied #2 overlays.
[  783.435179] bone-capemgr bone_capemgr.9: part_number 'bspm_P8_12_27', version 'N/A'
[  783.435256] bone-capemgr bone_capemgr.9: slot #8: generic override
[  783.435273] bone-capemgr bone_capemgr.9: bone: Using override eeprom data at slot 8
[  783.435289] bone-capemgr bone_capemgr.9: slot #8: 'Override Board Name,00A0,Override Manuf,bspm_P8_12_27'
[  783.435392] bone-capemgr bone_capemgr.9: slot #8: Requesting part number/version based 'bspm_P8_12_27-00A0.dtbo
[  783.435409] bone-capemgr bone_capemgr.9: slot #8: Requesting firmware 'bspm_P8_12_27-00A0.dtbo' for board-name 'Override Board Name', version '00A0'
[  783.436715] bone-capemgr bone_capemgr.9: slot #8: dtbo 'bspm_P8_12_27-00A0.dtbo' loaded; converting to live tree
[  783.442819] bone-capemgr bone_capemgr.9: slot #8: bspm_P8_12_27 conflict P8.12 (#7:GPIO_P8_12_0x37)
[  783.452333] bone-capemgr bone_capemgr.9: slot #8: Failed verification

Looks like something else loaded an overlay called 'GPIO_P8_12_0x37' and it conflicted.