mercury-parser/src/extractors/generic/lead-image-url/score-image.js

import {
  POSITIVE_LEAD_IMAGE_URL_HINTS_RE,
  NEGATIVE_LEAD_IMAGE_URL_HINTS_RE,
  GIF_RE,
  JPG_RE,
} from './constants'

import { PHOTO_HINTS_RE } from '../content/scoring/constants'

// Scores image urls based on a variety of heuristics.
export function scoreImageUrl(url) {
  url = url.trim()
  let score = 0

  if (POSITIVE_LEAD_IMAGE_URL_HINTS_RE.test(url)) {
    score = score + 20
  }

  if (NEGATIVE_LEAD_IMAGE_URL_HINTS_RE.test(url)) {
    score = score - 20
  }

  // TODO: We might want to consider removing this as
  // gifs are much more common/popular than they once were
  if (GIF_RE.test(url)) {
    score = score - 10
  }

  if (JPG_RE.test(url)) {
    score = score + 10
  }

  // PNGs are neutral.

  return score
}

// Alt attribute usually means non-presentational image.
export function scoreAttr($img) {
  if ($img.attr('alt')) {
    return 5
  } else {
    return 0
  }
}

// Look through our parent and grandparent for figure-like
// container elements, give a bonus if we find them
export function scoreByParents($img) {
  let score = 0
  const $figParent = $img.parents('figure').first()

  if ($figParent.length === 1) {
    score = score + 25
  }

  const $parent = $img.parent()
  let $gParent
  if ($parent.length === 1) {
    $gParent = $parent.parent()
  }

  [$parent, $gParent].forEach($node => {
    if (PHOTO_HINTS_RE.test(getSig($node))) {
      score = score + 15
    }
  })

  return score
}

// Look at our immediate sibling and see if it looks like it's a
// caption. Bonus if so.
export function scoreBySibling($img) {
  let score = 0
  const $sibling = $img.next()
  const sibling = $sibling.get(0)

  if (sibling && sibling.tagName === 'figcaption') {
    score = score + 25
  }

  if (PHOTO_HINTS_RE.test(getSig($sibling))) {
    score = score + 15
  }

  return score
}

export function scoreByDimensions($img) {
  let score = 0

  const width = parseFloat($img.attr('width'))
  const height = parseFloat($img.attr('height'))
  const src = $img.attr('src')

  // Penalty for skinny images
  if (width && width <= 50) {
    score = score - 50
  }

  // Penalty for short images
  if (height && height <= 50) {
    score = score - 50
  }

  if (width && height && !src.includes('sprite')) {
    const area = width * height
    if (area < 5000) { // Smaller than 50 x 100
      score = score - 100
    } else {
      score = score + Math.round(area/1000)
    }
  }

  return score
}

export function scoreByPosition($imgs, index) {
  return $imgs.length/2 - index
}

function getSig($node) {
  return `${$node.attr('class') || ''} ${$node.attr('id') || ''}`
}