Changing CSS Values with Javascript

2018-12-31 23:56发布

站内问答 / JavaScript
1759 9 6

It's easy to set inline CSS values with javascript. If I want to change the width and I have html like this:

<div style="width: 10px"></div>

All I need to do is:

document.getElementById('id').style.width = value;

It will change the inline stylesheet values. Normally this isn't a problem, because the inline style overrides the stylesheet. Example:

<style>
   #tId {
      width: 50%;
   }
</style>

<div id="tId"></div>

Using this Javascript:

document.getElementById('tId').style.width = "30%";

I get the following:

<style>
   #tId {
      width: 50%;
   }
</style>

<div id="tId" style="width: 30%";></div>

This is a problem, because not only do I not want to change inline values, If I look for the width before I set it, when I have:

<div id="tId"></div>

The value returned is Null, so if I have Javascript that needs to know the width of something to do some logic (I increase the width by 1%, not to a specific value), getting back Null when I expect the string "50%" doesn't really work.

So my question: I have values in a CSS style that are not located inline, how can I get these values? How can I modify the style instead of the inline values, given an id?

9条回答
伤终究还是伤i
2楼-- · 2019-01-01 00:14

This simple 32 lines gist lets you identify a given stylesheet and change its styles very easily:

var styleSheet = StyleChanger("my_custom_identifier");
styleSheet.change("darkolivegreen", "blue");
查看更多
0人赞 添加讨论(0) 举报
几人难应
3楼-- · 2019-01-01 00:27

I don't have rep enough to comment so I'll format an answer, yet it is only a demonstration of the issue in question.

It seems, when element styles are defined in stylesheets they are not visible to getElementById("someElement").style

This code illustrates the issue... Code from below on jsFiddle.

In Test 2, on the first call, the items left value is undefined, and so, what should be a simple toggle gets messed up. For my use I will define my important style values inline, but it does seem to partially defeat the purpose of the stylesheet.

Here's the page code...

<html>
  <head>
    <style type="text/css">
      #test2a{
        position: absolute;
        left: 0px;
        width: 50px;
        height: 50px;
        background-color: green;
        border: 4px solid black;
      }
      #test2b{
        position: absolute;
        left: 55px;
        width: 50px;
        height: 50px;
        background-color: yellow;
        margin: 4px;
      }
    </style>
  </head>
  <body>

  <!-- test1 -->
    Swap left positions function with styles defined inline.
    <a href="javascript:test1();">Test 1</a><br>
    <div class="container">
      <div id="test1a" style="position: absolute;left: 0px;width: 50px; height: 50px;background-color: green;border: 4px solid black;"></div>
      <div id="test1b" style="position: absolute;left: 55px;width: 50px; height: 50px;background-color: yellow;margin: 4px;"></div>
    </div>
    <script type="text/javascript">
     function test1(){
       var a = document.getElementById("test1a");
       var b = document.getElementById("test1b");
       alert(a.style.left + " - " + b.style.left);
       a.style.left = (a.style.left == "0px")? "55px" : "0px";
       b.style.left = (b.style.left == "0px")? "55px" : "0px";
     }
    </script>
  <!-- end test 1 -->

  <!-- test2 -->
    <div id="moveDownThePage" style="position: relative;top: 70px;">
    Identical function with styles defined in stylesheet.
    <a href="javascript:test2();">Test 2</a><br>
    <div class="container">
      <div id="test2a"></div>
      <div id="test2b"></div>
    </div>
    </div>
    <script type="text/javascript">
     function test2(){
       var a = document.getElementById("test2a");
       var b = document.getElementById("test2b");
       alert(a.style.left + " - " + b.style.left);
       a.style.left = (a.style.left == "0px")? "55px" : "0px";
       b.style.left = (b.style.left == "0px")? "55px" : "0px";
     }
    </script>
  <!-- end test 2 -->

  </body>
</html>

I hope this helps to illuminate the issue.

Skip

查看更多
0人赞 添加讨论(0) 举报
明月照影归
4楼-- · 2019-01-01 00:27

You can get the "computed" styles of any element.

IE uses something called "currentStyle", Firefox (and I assume other "standard compliant" browsers) uses "defaultView.getComputedStyle".

You'll need to write a cross browser function to do this, or use a good Javascript framework like prototype or jQuery (search for "getStyle" in the prototype javascript file, and "curCss" in the jquery javascript file).

That said if you need the height or width you should probably use element.offsetHeight and element.offsetWidth.

The value returned is Null, so if I have Javascript that needs to know the width of something to do some logic (I increase the width by 1%, not to a specific value)

Mind, if you add an inline style to the element in question, it can act as the "default" value and will be readable by Javascript on page load, since it is the element's inline style property:

<div style="width:50%">....</div>
查看更多
0人赞 添加讨论(0) 举报
不再属于我。
5楼-- · 2019-01-01 00:29

I don't know why the other solutions go through the whole list of stylesheets for the document. Doing so creates a new entry in each stylesheet, which is inefficient. Instead, we can simply append a new stylesheet and simply add our desired CSS rules there.

style=document.createElement('style');
document.head.appendChild(style);
stylesheet=style.sheet;
function css(selector,property,value)
{
    try{ stylesheet.insertRule(selector+' {'+property+':'+value+'}',stylesheet.cssRules.length); }
    catch(err){}
}

Note that we can override even inline styles set directly on elements by adding " !important" to the value of the property, unless there already exist more specific "!important" style declarations for that property.

查看更多
0人赞 添加讨论(0) 举报
不再属于我。
6楼-- · 2019-01-01 00:35

Gathering the code in the answers, I wrote this function that seems running well on my FF 25.

function CCSStylesheetRuleStyle(stylesheet, selectorText, style, value){
  /* returns the value of the element style of the rule in the stylesheet
  *  If no value is given, reads the value
  *  If value is given, the value is changed and returned
  *  If '' (empty string) is given, erases the value.
  *  The browser will apply the default one
  *
  * string stylesheet: part of the .css name to be recognized, e.g. 'default'
  * string selectorText: css selector, e.g. '#myId', '.myClass', 'thead td'
  * string style: camelCase element style, e.g. 'fontSize'
  * string value optionnal : the new value
  */
  var CCSstyle = undefined, rules;
  for(var m in document.styleSheets){
    if(document.styleSheets[m].href.indexOf(stylesheet) != -1){
     rules = document.styleSheets[m][document.all ? 'rules' : 'cssRules'];
     for(var n in rules){
       if(rules[n].selectorText == selectorText){
         CCSstyle = rules[n].style;
         break;
       }
     }
     break;
    }
  }
  if(value == undefined)
    return CCSstyle[style]
  else
    return CCSstyle[style] = value
}

This is a way to put values in the css that will be used in JS even if not understood by the browser. e.g. maxHeight for a tbody in a scrolled table.

Call :

CCSStylesheetRuleStyle('default', "#mydiv", "height");

CCSStylesheetRuleStyle('default', "#mydiv", "color", "#EEE");

查看更多
0人赞 添加讨论(0) 举报
呛了眼睛熬了心
7楼-- · 2019-01-01 00:38

Ok, it sounds like you want to change the global CSS so which will effictively change all elements of a peticular style at once. I've recently learned how to do this myself from a Shawn Olson tutorial. You can directly reference his code here.

Here is the summary:

You can retrieve the stylesheets via document.styleSheets. This will actually return an array of all the stylesheets in your page, but you can tell which one you are on via the document.styleSheets[styleIndex].href property. Once you have found the stylesheet you want to edit, you need to get the array of rules. This is called "rules" in IE and "cssRules" in most other browsers. The way to tell what CSSRule you are on is by the selectorText property. The working code looks something like this:

var cssRuleCode = document.all ? 'rules' : 'cssRules'; //account for IE and FF
var rule = document.styleSheets[styleIndex][cssRuleCode][ruleIndex];
var selector = rule.selectorText;  //maybe '#tId'
var value = rule.value;            //both selectorText and value are settable.

Let me know how this works for ya, and please comment if you see any errors.

查看更多
0人赞 添加讨论(0) 举报
1 2 下一页
登录 后发表回答
相关问题
查看全部
相关文章
查看全部
收藏的人(6)