wot-design/packages/input/src/calcTextareaHeight.js

Mobile UI components built on vue.js

let hiddenTextarea

const HIDDEN_STYLE = `
  height: 0 !important;
  visibility: hidden !important;
  overflow: hidden !important;
  position: absolute !important;
  z-index: -1000 !important;
  top: 0 !important;
  right: 0 !important;
`

const CONTEXT_STYLE = [
  'letter-spacing',
  'line-height',
  'padding-top',
  'padding-bottom',
  'font-family',
  'font-size',
  'text-rendering',
  'text-transform',
  'width',
  'text-indent',
  'padding-left',
  'padding-right',
  'border-width',
  'box-sizing'
]

const calculateNodeStyling = element => {
  const style = window.getComputedStyle(element)
  const boxSizing = style.getPropertyValue('box-sizing')

  const paddingSize = parseFloat(style.getPropertyValue('padding-bottom')) + parseFloat(style.getPropertyValue('padding-top'))
  const borderSize = parseFloat(style.getPropertyValue('border-bottom-width')) + parseFloat(style.getPropertyValue('border-top-width'))

  const contextStyle = CONTEXT_STYLE.map(name => `${name}: ${style.getPropertyValue(name)}`).join(';')

  return { contextStyle, paddingSize, borderSize, boxSizing }
}

export default function calcTextareaHeight (element, minRows = 1, maxRows = null) {
  hiddenTextarea = document.createElement('textarea')
  document.body.appendChild(hiddenTextarea)

  let {
    paddingSize,
    borderSize,
    boxSizing,
    contextStyle
  } = calculateNodeStyling(element)

  hiddenTextarea.setAttribute('style', `${contextStyle};${HIDDEN_STYLE}}`)
  hiddenTextarea.value = element.value || element.placeholder || ''

  let height = hiddenTextarea.scrollHeight
  const result = {}

  if (boxSizing === 'border-box') {
    height = height + borderSize
  } else if (boxSizing === 'content-box') {
    height = height - paddingSize
  }

  hiddenTextarea.value = ''
  let singleRowHeight = hiddenTextarea.scrollHeight - paddingSize

  let minHeight = singleRowHeight * minRows
  if (boxSizing === 'border-box') {
    minHeight = minHeight + paddingSize + borderSize
  }
  height = Math.max(minHeight, height)
  result.minHeight = `${minHeight}px`

  if (maxRows !== null) {
    let maxHeight = singleRowHeight * maxRows
    if (boxSizing === 'border-box') {
      maxHeight = maxHeight + paddingSize + borderSize
    }
    height = Math.min(maxHeight, height)
  }
  result.height = `${height}px`
  hiddenTextarea.parentNode && hiddenTextarea.parentNode.removeChild(hiddenTextarea)
  hiddenTextarea = null
  return result
}