window.jQuery = function(nodeOrSelector) {

  let nodes = {};

  if (typeof nodeOrSelector === 'string') {

    let temp = document.querySelectorAll(nodeOrSelector);

    for (let i=0; i<temp.length; i++) {

      nodes[i] = temp[i];

      nodes.length = temp.length;

    }

  } else if ( nodeOrSelector instanceof Node ) {

    nodes = {0: nodeOrSelector, length: 1};

  }

  nodes.addClass = function(classes) {

    if (typeof classes === 'string') {

      let temp = classes;

      classes = Array(temp);

    }

    classes.forEach((value) => {

      for (let i=0; i < nodes.length; i++) {

        nodes[i].classList.add(value);

      };

    });

  };

  nodes.setText = function(text) {

    for (let i=0; i<nodes.length; i++) {

      nodes[i].textContent = text;

    }

  };

  return nodes;

};

window.$ = jQuery;

var $div = $('div');

$div.addClass('red'); // 可将所有 div 的 class 添加一个 red

$div.setText('hi'); // 可将所有 div 的 textContent 变为 hi