借鉴Element-ui中源码方法实现H5页面中textarea自适应高度方法

直接上方法和使用吧（vue项目）

• 方法(在项目的公共方法中，添加一个js文件)

  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-weight',
    'font-size',
    'text-rendering',
    'text-transform',
    'width',
    'text-indent',
    'padding-left',
    'padding-right',
    'border-width',
    'box-sizing',
  ];
  
  function calculateNodeStyling(targetElement) {
    const style = window.getComputedStyle(targetElement);
  
    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(
    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;
  }
  

• 使用(我这里是使用vue中watch来触发方法)

  <textarea
    ref="textarea"
    v-model="machine.acceptdtl"
    :style="{'height': height}"
    maxlength="1000"
    @input="inputRule"
    @focus="onFocus('333')"
    @blur="onBlur"
  />
  

  watch: {
      'machine.acceptdtl': {
        handler: function() {
          this.getHeight();
        },
      },
    },
  

  getHeight() {
    this.height = calcTextareaHeight(this.$refs.textarea, 1, null).height;
  },