calculate maximum IG lightbox width given image dimensions

maxLightboxWidth.js

// Constants
const MAX_PLACEHOLDER_WIDTH = 640
const MAX_PLACEHOLDER_HEIGHT = 640
const SIDEBAR_WIDTH = 320

function calcPlaceholderWidth(imageWidth, imageHeight) {
    const aspectRatio = imageHeight / imageWidth

    let placeholderWidth

    if (aspectRatio <= 1) { // wide and square images, we want them to fill the available horizontal space
      placeholderWidth = MAX_PLACEHOLDER_WIDTH
    } else { // tall images, we want them to fill the available vertical space
      placeholderWidth = ((imageWidth * MAX_PLACEHOLDER_HEIGHT) / imageHeight)
    }

    return Math.min(placeholderWidth, MAX_PLACEHOLDER_WIDTH)
}

function calcMaxLightboxWidth(imageWidth, imageHeight) {
    return calcPlaceholderWidth(imageWidth, imageHeight) + SIDEBAR_WIDTH
}

console.log(calcMaxLightboxWidth(1080, 1350))
console.log(calcMaxLightboxWidth(1080, 1080))
console.log(calcMaxLightboxWidth(1080, 810))