四种方法：
1.通过id获取
<!DOCTYPE html>
<html><head><meta charset="UTF-8"><title></title></head><body><div id="ch"><span>长城</span><b>故宫</b></div><p class="zh">黄河</p><p class="zh">黄河</p><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><script>var element = document.getElementById("ch");/*获取id为"ch"的元素对应的JavaScript对象*/console.log(element);</script></body>
</html>
2.通过class名获取：
<!DOCTYPE html>
<html><head><meta charset="UTF-8"><title></title></head><body><div id="ch"><span>长城</span><b>故宫</b></div><p class="zh">黄河</p><p class="zh">黄河</p><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><script>var elements = document.getElementsByClassName("zh");for (var i in elements) {console.log(elements[i]);/*由于class名可以有多个，则可以用数组遍历，（加强for循环）*/}</script></body>
</html>
3.通过标签名获取：
<!DOCTYPE html>
<html><head><meta charset="UTF-8"><title></title></head><body><div id="ch"><span>长城</span><b>故宫</b></div><p class="zh">黄河</p><p class="zh">黄河</p><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><script>elements = document.getElementsByTagName("p");for (var i in elements) {console.log(elements[i]);}</script></body>
</html>
4.通过name值获取：
<!DOCTYPE html>
<html><head><meta charset="UTF-8"><title></title></head><body><div id="ch"><span>长城</span><b>故宫</b></div><p class="zh">黄河</p><p class="zh">黄河</p><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><input type = "checkbox" name="hobby"/><script>elements = document.getElementsByName("hobby");for (var i in elements) {console.log(elements[i]);}</script></body>
</html>