Overriding !important style

Question

There are a couple of simple one-liners you can use to do this.

1. Set a "style" attribute on the element:

   element.setAttribute('style', 'display:inline !important');

or...

2. Modify the cssText property of the style object:

   element.style.cssText = 'display:inline !important';

Either will do the job.

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I've written a jQuery plugin called "important" to manipulate !important rules in elements, : http://github.com/premasagar/important

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Edit: As shared in the comments, the standard CSSOM interface (the API for JavaScript to interact with CSS) provides the setProperty method:

element.style.setProperty(propertyName, value, priority);

E.g:

document.body.style.setProperty('background-color', 'red', 'important');

element.style has a setProperty method that can take the priority as a third parameter:

element.style.setProperty("display", "inline", "important")

It didn't work in old IEs but it should be fine in current browsers.

I believe the only way to do this it to add the style as a new CSS declaration with the '!important' suffix. The easiest way to do this is to append a new <style> element to the head of document:

function addNewStyle(newStyle) {
    var styleElement = document.getElementById('styles_js');
    if (!styleElement) {
        styleElement = document.createElement('style');
        styleElement.type = 'text/css';
        styleElement.id = 'styles_js';
        document.getElementsByTagName('head')[0].appendChild(styleElement);
    }
    styleElement.appendChild(document.createTextNode(newStyle));
}

addNewStyle('td.EvenRow a {display:inline !important;}')

The rules added with the above method will (if you use the !important suffix) override other previously set styling. If you're not using the suffix then make sure to take concepts like 'specificity' into account.

Building on @Premasagar's excellent answer; if you don't want to remove all the other inline styles use this

//accepts the hyphenated versions (i.e. not 'cssFloat')
addStyle(element, property, value, important) {
    //remove previously defined property
    if (element.style.setProperty)
        element.style.setProperty(property, '');
    else
        element.style.setAttribute(property, '');

    //insert the new style with all the old rules
    element.setAttribute('style', element.style.cssText +
        property + ':' + value + ((important) ? ' !important' : '') + ';');
}

_{Can't use removeProperty() because it wont remove !important rules in Chrome.
Can't use element.style[property] = '' because it only accepts camelCase in FireFox.}

If you want to update / add single style in DOM Element style attribute you can use this function:

function setCssTextStyle(el, style, value) {
  var result = el.style.cssText.match(new RegExp("(?:[;\\s]|^)(" +
      style.replace("-", "\\-") + "\\s*:(.*?)(;|$))")),
    idx;
  if (result) {
    idx = result.index + result[0].indexOf(result[1]);
    el.style.cssText = el.style.cssText.substring(0, idx) +
      style + ": " + value + ";" +
      el.style.cssText.substring(idx + result[1].length);
  } else {
    el.style.cssText += " " + style + ": " + value + ";";
  }
}

style.cssText is supported for all major browsers.

Use case example:

var elem = document.getElementById("elementId");
setCssTextStyle(elem, "margin-top", "10px !important");

Here is link to demo