whole_func_string: function setAttr(el, attrName, attrVal) {
    if (attrVal === undefined) {
      el.removeAttribute(attrName);
    } else {
      el.setAttribute(attrName, attrVal);
    }
  }
func_code_string: function setAttr(el, attrName, attrVal) {
    if (attrVal === undefined) {
      el.removeAttribute(attrName);
    } else {
      el.setAttribute(attrName, attrVal);
    }
  }
func_documentation_string: 设置HTML元素属性值
  @param {HTMLElement} el 目标元素
  @param {String} attrName 目标属性名称
  @param {String} attrVal 目标属性值