cannot read property 'x' of unde

/*
* @param  {string} dir    'x' || 'y'
*/
updateIndex = (offset, dir, cb) => {
    if(offset === undefined || this.internals.offset === undefined){
    return;
}
const state = this.state
let index = state.index
const diff = offset[dir] - this.internals.offset[dir]