Vue中textarea自适应高度方案的实现

resizeTextarea() {
  if (this.$isServer) return;
  const { autosize, type } = this;
  if (type !== 'textarea') return;
  if (!autosize) {
    this.textareaCalcStyle = {
      minHeight: calcTextareaHeight(this.$refs.textarea).minHeight
    };
    return;
  }
  const minRows = autosize.minRows;
  const maxRows = autosize.maxRows;

  this.textareaCalcStyle = calcTextareaHeight(this.$refs.textarea, minRows, maxRows);
}

export default function calcTextareaHeight(
  targetElement,
  minRows = 1,
  maxRows = null
) {
  if (!hiddenTextarea) {
    hiddenTextarea = document.createElement('textarea');
    document.body.appendChild(hiddenTextarea);
  }

  let {
    paddingSize,
    borderSize,
    boxSizing,
    contextStyle
  } = calculatenodeStyling(targetElement);

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

  if (minRows !== null) {
    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;
};

if (!hiddenTextarea) {
  hiddenTextarea = document.createElement('textarea');
  document.body.appendChild(hiddenTextarea);
}

init() {
  this.initAutoResize()
},
initAutoResize () {
  this.autoResize && this.$nextTick(this.calcResize)
}

calcResize() {
  this.resetHeight()
  this.calcTextareaH()
},

resetHeight() {
  this.height = 'auto'
},

calcTextareaH() {
  let contentHeight = this.calcContentHeight()
  this.height = this.calcHeightChange(contentHeight) + 'px'
  if (this.needUpdateRows(contentHeight)) {
    this.updateRows(contentHeight)
  }
  this.oldContentHeight = contentHeight
},

calcContentHeight () {
  const { paddingSize } = this.calcNodeStyle(this.$el)
  return this.$el.scrollHeight - paddingSize
},

computed: {
  ...
  oneRowsHeight() {
    return this.calcContentHeight() / Number(this.rows) || 0
  }
  ...
}

this.oldContentHeight = contentHeight

needUpdateRows(newContentHeight) {
  return this.oldContentHeight !== newContentHeight
},

updateRows(contentHeight) {
  this.$emit('getRows', Math.round(contentHeight / this.oneRowsHeight))
}