I'm calling makeALine function inside of lines function.
And I a trying to save line in makeALine function, using this keyword. 
But it says this is undefined.
I have no idea why it is undefined.
Anyone help?
function makeALine(setOfDots) {
    let line = {
        model: new makerjs.paths.Line(setOfDots)
    }
    console.log(this) //undefined
    this.paths = line;
}
function lines(obj) {
    for (let [key, value] of Object.entries(obj)) {
        console.log('value', value)
        let lineType = key.includes(LINE) ? makeALine(value) : null;
        lineTypes.push(lineType)
    }
    console.log(lineTypes)
}
