CODEWITHSUNDEEP
javascript
DemonWareXT
DemonWareXT

Reputation: 531

Detect Element.Style changes with Javascript

I am at the moment working on a little extension to enhance a website namely the google plus post box. I want to move it to the very left of the monitor.

This post box however resets its values every time it is opened.

Basically I would like to kill off that behavior, and thought I could just monitor the element for element.style changes, and overwrite them again. However DOMAttrModified seems not to work for stuff like that

Additionally to that I have found that when the post box is closed it ceases to exist oO?

Maybe someone here has an idea how to tackle this I could of course just loop an operation that sets the style every second or so. but no thanks XD

thanks a lot for helping :)

Upvotes: 9

Views: 11313

Answers (2)

Roko C. Buljan
Roko C. Buljan

Reputation: 206593

To get you quickly started with using Mutation Observer
here's a small reusable function

/**
 * Mutation Observer Helper function
 * //developer.mozilla.org/en-US/docs/Web/API/MutationObserver/observe
 * @param {string} sel The DOM selector to watch 
 * @param {object} opt MutationObserver options 
 * @param {function} cb Pass Mutation object to a callback function
 */
const Observe = (sel, opt, cb) => {
  const Obs = new MutationObserver((m) => [...m].forEach(cb));
  document.querySelectorAll(sel).forEach(el => Obs.observe(el, opt));
};

To track only attribute "style" changes on some class="item" Elements, use like:

Observe(".item", {
  attributesList: ["style"], // Only the "style" attribute
  attributeOldValue: true,   // Report also the oldValue
}, (m) => {
  console.log(m);            // Mutation object
});

To watch for all attributes changes, instead of the attributesList Array use :

attributes: true

If needed, here's an example:

/**
 * Mutation Observer Helper function
 * //developer.mozilla.org/en-US/docs/Web/API/MutationObserver/observe
 * @param {string} sel The DOM selector to watch 
 * @param {object} opt MutationObserver options 
 * @param {function} cb Pass Mutation object to a callback function
 */
const Observe = (sel, opt, cb) => {
  const Obs = new MutationObserver((m) => [...m].forEach(cb));
  document.querySelectorAll(sel).forEach(el => Obs.observe(el, opt));
};

// DEMO TIME:
Observe("#test", {
  attributesList: ["style"], 
  attributeOldValue: true,
}, (m) => {
  console.log(`
    Old value: ${m.oldValue}
    New value: ${m.target.getAttribute(m.attributeName)}
  `);
});

const EL_test = document.querySelector("#test");
EL_test.addEventListener("input", () => EL_test.style.cssText = EL_test.value);
EL_test.style.cssText = EL_test.value;
* {margin:0;}
textarea {width: 60%;height: 50px;}
<textarea id="test">
background: #0bf;
color: #000;
</textarea>

Upvotes: 5

Jan Turoň
Jan Turoň

Reputation: 32922

Mutation events are deprecated, DOMAttrModified is not and will not be supported by webkit browsers. Use Mutation Observers instead. Alternatively, you can try this workaround.

Upvotes: 9

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