querySelector vs. querySelectorAll

问题

I have some trouble in creating a selector in javascript.
This is my code:

function __(selector){

    var self = {};
    self.selector = selector;

    if(typeof selector == 'object'){
       self.element = self.selector;
    }else{
       self.element = document.querySelector(self.selector);
    }

   // make a .css method to an element
    self.css = function(propval){
       return Object.assign(self.element.style,propval);
    }

   return self;
}

And my html file

<script src="js/selector.js"></script>
<script>
     window.onload = function(){
      __('p').css({'color':'red'});
    }
</script>

<p>Hello</p>
<p>World</p>
<p>John</p>

The code above will only apply the .css method in the first <p> element. It's because I only used querySelector. Because querySelector only selects the first element found. And querySelectorAll selects all elements found. But when I try to change my selector to querySelectorAll It doesnt work for me anymore.

回答1:

Well, the reason is querySelectorAll() returns a NodeList of the selected elements and assigning CSS to a NodeList wouldn't make much of an effect

That said, essentially you need a way to handle the case of a single element and a many in the same way

From the top of my head, a simple solution could be to always use an arrays or the NodeList and forEach() over them since both implement this method, like so:

function __(selector){

    var self = {};
    self.selector = selector;

    if(typeof selector == 'object'){
       self.elements = [self.selector];
    }else{
       self.elements = document.querySelectorAll(self.selector);
    }

    // make a .css method to an element
    self.css = function(propval){
       self.elements.forEach(function(element){
         Object.assign(element.style, propval);
       });
    }

   return self;
}

回答2:

I'm no expert here so this can probably be optimized, but with an array/list of objects you need to loop through each one

Updated with a polyfill so this one work on at least IE11/10/9

function __(selector){

    var self = {};
    self.selector = selector;

    if(typeof selector == 'object'){
       self.element = self.selector;
    }else{
       self.elements = document.querySelectorAll(self.selector);
    }

   // make a .css method to an element
    self.css = function(propval){
       if (self.elements) {
         for (var i = 0; i < self.elements.length; i++) {
           Object.assign(self.elements[i].style,propval);
         }
         return;
       } else {
         Object.assign(self.element.style,propval);
       }
    }

   return self;
}

if (typeof Object.assign != 'function') {
  Object.assign = function (target, varArgs) { // .length of function is 2
    'use strict';
    if (target == null) { // TypeError if undefined or null
      throw new TypeError('Cannot convert undefined or null to object');
    }

    var to = Object(target);

    for (var index = 1; index < arguments.length; index++) {
      var nextSource = arguments[index];

      if (nextSource != null) { // Skip over if undefined or null
        for (var nextKey in nextSource) {
          // Avoid bugs when hasOwnProperty is shadowed
          if (Object.prototype.hasOwnProperty.call(nextSource, nextKey)) {
            to[nextKey] = nextSource[nextKey];
          }
        }
      }
    }
    return to;
  };
}

<p>Hello</p>
<p>World</p>
<p>John</p>
<div>Albert</div>
<script>
     window.onload = function(){
      __('p').css({'color':'red'});
      __(document.querySelector('div')).css({'color':'blue'});
    }
</script>

来源：https://stackoverflow.com/questions/41086336/queryselector-vs-queryselectorall

标签

javascript

css-selectors