Javascript：单击事件处理程序不起作用

Question

 function check() { var para = document.getElementsByTagName("p"); para[0].style.fontSize = 20; }

 <p>This a paragraph</p> <p>This a paragraph</p> <p>This a paragraph</p> <p>This a paragraph</p> <button onClick="check()">Check</button>

please check the script section I am not able to find any error please help me this

Answer 1

Specify font size in pixels inside string instead of using number 20. Also move the script tag to bottom of body tag.

Please find the working snippit below:

 function check() { var para=document.getElementsByTagName("p"); para[0].style.fontSize= '20px' ; }

 <p>This a paragraph</p> <p>This a paragraph</p> <p>This a paragraph</p> <p>This a paragraph</p> <button onclick="check()">Check</button>

Answer 2

For each Tag P must use like this...

js

function check() {
  var s=document.getElementsByTagName('p');
  for(i=0;i<s.length;i++)
  {
    s[i].setAttribute("style","font-size:20px");
  }
}

View

<p>This a paragraph</p>
<p>This a paragraph</p>
<p>This a paragraph</p>
<p>This a paragraph</p>
<button onClick="check()">Check</button>

Answer 3

you have to define the size in string with px,em,% behind and wrap it with quote

para[0].style.fontSize = 20;

to

para[0].style.fontSize = "20px";