DOM Element Width before Appended to DOM

问题

I'm sure the answer is no, but is it possible to determine the width of an element before it is appended to the DOM?

Once it's appended, I know I can use offsetWidth and offsetHeight.

Thanks

回答1:

The trick is to show the element (display:block) but also hide it (visibility:hidden) and to set it’s position to absolute so that it doesn’t affect the page flow.

The MooTools Element.Measure class does this, as Oscar mentioned.

回答2:

The Mootools Element.Measure functionality that Oscar mentioned is awesome. For those that use jQuery, here's a quick plugin that accomplishes the same thing:

$.fn.measure = (fn)->
  el = $(this).clone(false)
  el.css
    visibility: 'hidden'
    position:   'absolute'
  el.appendTo('body')
  result = fn.apply(el)
  el.remove()
  return result

You can call it like this, making sure to return the value (thanks Sam Fen for pointing that out!):

width = $('.my-class-name').measure( function(){ return this.width() } )

回答3:

What you can do with MooTools is use the Element.Measure class - meaning, you inject the element to the DOM, but keep it hidden. Now, you can measure the element without actually showing it.

http://mootools.net/docs/more/Element/Element.Measure

回答4:

It is not possible, at least not accurately, because styling affects these properties, and where it's put determines how it is styled and what rules affect it.

For example placing a <p></p> in the page would by default be the width of the body if appended as a child to it, but if you appeneded it inside for example a <div style="width: 100px;"></div>, then you see how that quickly changes things.

回答5:

Modified the code a bit. Here is a pure JS solution:

function measure(el, fn) {
    var pV = el.style.visibility, 
        pP = el.style.position;
        
    el.style.visibility = 'hidden';
    el.style.position = 'absolute';
    
    document.body.appendChild(el);
    var result = fn(el);
    el.parentNode.removeChild(el);
    
    el.style.visibility = pV;
    el.style.position = pP;
    return result;
}

var div = document.createElement('div');
div.innerHTML = "<p>Hello</p><br/>";

alert(div.offsetHeight); // 0

alert(measure(div, function(el){return el.offsetHeight})); // 68

回答6:

/**
 * Get bounding client rect for an element (not exists at current DOM tree)
 * @param {!HTMLElement} el
 * @return {!Promise<!ClientRect>}
 */
function getElementRect(el) {
  return new Promise(resolve => {
    const element = el.cloneNode(true);
    element.style.visibility = "hidden";
    element.style.position = "absolute";
    document.body.appendChild(element);

    resolve(element.getBoundingClientRect());
    element.remove();
  });
}

const div = /** @type {!HTMLElement} */ (document.createElement("div"));
div.innerHTML = "<p>Hello</p><br/>";

// Execute
(async () => {
  const rect = await getElementRect(div);
  console.log(rect.width);
})();

DEMO

来源：https://stackoverflow.com/questions/2921428/dom-element-width-before-appended-to-dom

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javascript

jquery

html

mootools