querySelector search immediate children

问题:

I have some jquery-like function:

function(elem) {
    return $('> someselector', elem);
};

The question is how can i do the same with querySelector()?

The problem is > selector in querySelector() requires parent to be explicitly specified. Is there any workaround?

回答1:

Though it's not a full answer, you should keep an eye on the W3C Selector API v.2 which is already available in Google Chrome and Safari 7.x (both desktop and mobile), but as far as I have tested, still not there in Firefox and IE.

function(elem) {
  return elem.querySelectorAll(':scope > someselector');
};

回答2:

You can't. There's no selector that will simulate your starting point.

The way jQuery does it (more because of a way that qsa behaves that is not to their liking), is that they check to see if elem has an ID, and if not, they temporarily add an ID, then create a full selector string.

Basically you'd do:

var sel = '> someselector';
var hadId = true;
if( !elem.id ) {
    hadID = false;
    elem.id = 'some_unique_value';
}

sel = '#' + elem.id + sel;

var result = document.querySelectorAll( sel );

if( !hadId ) {
    elem.id = '';
}

This certainly isn't jQuery code, but from what I remember, it is basically what they do. Not just in this situation, but in any situation where you're running a selector from the context of a nested element.

Source code for Sizzle

回答3:

Complete :scope polyfill

As avetisk has mentioned Selectors API 2 uses :scope pseudo-selector.
To make this work in all browsers (that support querySelector) here is the polyfill

(function(doc, proto) {
  try { // check if browser supports :scope natively
    doc.querySelector(':scope body');
  } catch (err) { // polyfill native methods if it doesn't
    ['querySelector', 'querySelectorAll'].forEach(function(method) {
      var nativ = proto[method];
      proto[method] = function(selectors) {
        if (/(^|,)\s*:scope/.test(selectors)) { // only if selectors contains :scope
          var id = this.id; // remember current element id
          this.id = 'ID_' + Date.now(); // assign new unique id
          selectors = selectors.replace(/((^|,)\s*):scope/g, '$1#' + this.id); // replace :scope with #ID
          var result = doc[method](selectors);
          this.id = id; // restore previous id
          return result;
        } else {
          return nativ.call(this, selectors); // use native code for other selectors
        }
      }
    });
  }
})(window.document, Element.prototype);

Usage

node.querySelector(':scope > someselector');
node.querySelectorAll(':scope > someselector');

---

For historical reasons, my previous solution

Based on all answers

// Caution! Prototype extending
Node.prototype.find = function(selector) {
    if (/(^\s*|,\s*)>/.test(selector)) {
        if (!this.id) {
            this.id = 'ID_' + new Date().getTime();
            var removeId = true;
        }
        selector = selector.replace(/(^\s*|,\s*)>/g, '$1#' + this.id + ' >');
        var result = document.querySelectorAll(selector);
        if (removeId) {
            this.id = null;
        }
        return result;
    } else {
        return this.querySelectorAll(selector);
    }
};

Usage

elem.find('> a');

回答4:

If you know the tag name of the element that you’re looking into, then you can use it in the selector to achieve what you want.

For example if you have a <select> that has <option>s and <optgroups>, and you only want the <option>s that are its immediate children, not the ones inside <optgoups>:

<select>
  <option>iPhone</option>
  <optgroup>
    <option>Nokia</option>
    <option>Blackberry</option>
  </optgroup>
</select>

So, having a reference to the select element, you can — surprisingly — get its immediate children like this:

selectElement.querySelectorAll('select > option')

It seems to work in Chrome, Safari, and Firefox, but didn’t test in IEs. =/

回答5:

CLAIM

Personally I would take the answer from patrick dw, and +1 his answer, my answer is for seeking alternative solution. I don't think it deserves a downvote.

Here is my attempt :

function q(elem){
    var nodes = elem.querySelectorAll('someSeletor');
    console.log(nodes);
    for(var i = 0; i < nodes.length; i++){
        if(nodes[i].parentNode === elem) return nodes[i];
    }
}

see http://jsfiddle.net/Lgaw5/8/

回答6:

That worked for me:

Node.prototype.search = function(selector)
{
    if (selector.indexOf('@this') != -1)
    {
        if (!this.id)
            this.id = "ID" + new Date().getTime(); 
        while (selector.indexOf('@this') != -1)
            selector = selector.replace('@this', '#' + this.id);
        return document.querySelectorAll(selector);
    } else 
        return this.querySelectorAll(selector);
};

you will have to pass the @this keywork before the > when you want to search for immediate children.

回答7:

The following is a simplified, generic method for running any CSS selector query over only direct children - it also accounts for combined queries, like "foo[bar], baz.boo":

var count = 0;
function queryChildren(element, selector) {
  var id = element.id,
      guid = element.id = id || 'query_children_' + count++,
      attr = '#' + guid + ' > ',
      selector = attr + (selector + '').replace(',', ',' + attr, 'g');
  var result = element.parentNode.querySelectorAll(selector);
  if (!id) element.removeAttribute('id');
  return result;
}


*** Example Use ***

queryChildren(someElement, '.foo, .bar[xyz="123"]');

回答8:

There’s a query-relative lib, which is quite handy replacement for query-selector. It polyfills children selector '> *' and :scope (inc. IE8), as well as normalizes :root selector. Also it provides some special relative pseudos like :closest, :parent, :prev, :next, just in case.

回答9:

If you want to eventually find direct children (and not e.g. > div > span), you can try Element.matches():

const elems = Array.from(elem.children).filter(e => e.matches('.my-class'))

回答10:

check if element have id else add random id and do search based on it

function(elem) {
      if(!elem.id)
          elem.id = Math.random().toString(36).substr(2, 10);
      return elem.querySelectorAll(elem.id + ' > someselector');
    };

will do same thing as

$("> someselector",$(elem))