lineIntersectsPolygon

const { checkIntersection } = require('line-intersect')

const playerLine = [
  { x: 10, y: 10 }, // Player current pos
  { x: 30, y: 10 }  // Player target pos
]

const floorPolygon = [
  { x: 0, y: 0 },
  { x: 20, y: 0 },
  { x: 20, y: 20 },
  { x: 0, y: 20 }
]

function getPointsArr (obj, i) {
  const j = (i + 1) % obj.length
  return [ obj[i].x, obj[i].y, obj[j].x, obj[j].y ]
}

function lineIntersectsPolygon (line, polygon) {
  // Convert line to points array
  const linePoints = getPointsArr(line, 0)

  // Check each edge of polygon
  for (let i = 0; i < polygon.length; i++) {
    const polyPoints = getPointsArr(polygon, i)
    const { type, point } = checkIntersection(...linePoints, ...polyPoints)
    if (type === 'intersecting') {
      return point
    }
  }
  return false
}

console.log(lineIntersectsPolygon(playerLine, floorPolygon))