将 getElementById 替换为 getElementsByClassName

Question

我想修改下面的 JavaScript 来选择class name，而不是element id：

https://github.com/sarathsaleem/grained/blob/master/grained.js

然后理想地初始化，如下所示：

grained(".classname", options);

Answer 1

Sarath Saleem 的 grained.js 的这个修改版本获取具有给定类名选择器（即“.foo”）的所有元素，并为它们提供指定的噪声背景。这段代码我没怎么测试过，所以从效率上绝对不是生产质量。关键是将element 变量更改为elements 并使用document.getElementsByClassName，其中定义了新命名的elements 变量。这将返回具有给定类（即“foo”）的所有 HTML 元素的 HTMLCollection。然后，在设置元素的position 和overflow 属性的部分，使用for 循环并遍历HTMLCollection 为每个找到的具有给定类的元素设置position 和overflow 属性。
注意：grained.js 文件的底部是我调用grained 函数的地方。

此外，我调整了使用以前命名为 elementId 变量的位置，以使用基于给定类名的新 elementClass 变量。

您可以在 grained.js iife 之后的任何位置执行此操作，因为它在之后的全局命名空间中。

/*! Grained.js
* Author : Sarath Saleem  - https://github.com/sarathsaleem
* MIT license: http://opensource.org/licenses/MIT
* GitHub : https://github.com/sarathsaleem/grained
* v0.0.1
*/
(function (window, doc) {

    "use strict";

    function grained(ele, opt) {

        var elements = null,
            elementClass = null,
            selectorElement = null;

       //1
        if (typeof ele === 'string') {
            elements = doc.getElementsByClassName(ele.split('.')[1]);
        }
       //1
        if (!elements) {
            console.error('Grained: cannot find any elements with class ' + ele);
            return;
        } else {
            elementClass = elements[0].className;
        }

      var elementsLength = elements.length
      for( var i = 0; i < elementsLength; i++) {
        //set style for parent
        if (elements[i].style.position !== 'absolute') {
            elements[i].style.position = 'relative';
        }
        elements[i].style.overflow = 'hidden';
      };

        var prefixes = ["", "-moz-", "-o-animation-", "-webkit-", "-ms-"];

        //default option values
        var options = {
            animate: true,
            patternWidth: 100,
            patternHeight: 100,
            grainOpacity: 0.1,
            grainDensity: 1,
            grainWidth: 1,
            grainHeight: 1,
            grainChaos: 0.5,
            grainSpeed: 20

        };

        Object.keys(opt).forEach(function (key) {
            options[key] = opt[key];
        });


        var generateNoise = function () {
            var canvas = doc.createElement('canvas');
            var ctx = canvas.getContext('2d');
            canvas.width = options.patternWidth;
            canvas.height = options.patternHeight;
            for (var w = 0; w < options.patternWidth; w += options.grainDensity) {
                for (var h = 0; h < options.patternHeight; h += options.grainDensity) {
                    var rgb = Math.random() * 256 | 0;
                    ctx.fillStyle = 'rgba(' + [rgb, rgb, rgb, options.grainOpacity].join() + ')';
                    ctx.fillRect(w, h, options.grainWidth, options.grainHeight);
                }
            }
            return canvas.toDataURL('image/png');
        };

        function addCSSRule(sheet, selector, rules, index) {
            var ins = '';
            if (selector.length) {
                ins = selector + "{" + rules + "}";
            } else {
                ins = rules;
            }

            if ("insertRule" in sheet) {
                sheet.insertRule(ins, index);
            } else if ("addRule" in sheet) {
                sheet.addRule(selector, rules, index);
            }
        }


        var noise = generateNoise();

        var animation = '',
            keyFrames = ['0%:-10%,10%', '10%:-25%,0%', '20%:-30%,10%', '30%:-30%,30%', '40%::-20%,20%', '50%:-15%,10%', '60%:-20%,20%', '70%:-5%,20%', '80%:-25%,5%', '90%:-30%,25%', '100%:-10%,10%'];

        var pre = prefixes.length;
        while (pre--) {
            animation += '@' + prefixes[pre] + 'keyframes grained{';
            for (var key = 0; key < keyFrames.length; key++) {
                var keyVal = keyFrames[key].split(':');
                animation += keyVal[0] + '{';
                animation += prefixes[pre] + 'transform:translate(' + keyVal[1] + ');';
                animation += '}';
            }
            animation += '}';
        }

        //add animation keyframe
        var animationAdded = doc.getElementById('grained-animation');
        if (animationAdded) {
            animationAdded.parentElement.removeChild(animationAdded);
        }
        var style = doc.createElement("style");
        style.type = "text/css";
        style.id = 'grained-animation';
        style.innerHTML = animation;
        doc.body.appendChild(style);

        //add custimozed style
        var styleAdded = doc.getElementById('grained-animation-' + elementClass);
        if (styleAdded) {
            styleAdded.parentElement.removeChild(styleAdded);
        }

        style = doc.createElement("style");
        style.type = "text/css";
        style.id = 'grained-animation-' + elementClass;
        doc.body.appendChild(style);

        var rule = 'background-image: url(' + noise + ');';
        rule += 'position: absolute;content: "";height: 300%;width: 300%;left: -100%;top: -100%;';
        pre = prefixes.length;
        if (options.animate) {
            while (pre--) {
                rule += prefixes[pre] + 'animation-name:grained;';
                rule += prefixes[pre] + 'animation-iteration-count: infinite;';
                rule += prefixes[pre] + 'animation-duration: ' + options.grainChaos + 's;';
                rule += prefixes[pre] + 'animation-timing-function: steps(' +options.grainSpeed + ', end);';
            }
        }

        //selecter element to add grains
        selectorElement = '.' + elementClass + '::before';


        addCSSRule(style.sheet, selectorElement, rule, 0);


    }

    window.grained = grained;
    //END
})(window, document);

grained('.foo', {});

<!doctype html>
<html>
   <head>
      <title>Example</title>
      <style>
         .foo {
            height: 100px;
            width: 100px;
         }
      </style>
   </head>
   <body>
      <div class="foo">
         <div class="contents">
            <p>Hello World</p>
         </div>
      </div>
      <p>No Noise For Me!</p>
      <div class="foo">
         <div class="contents">
            <p>Hello World</p>
         </div>
      </div>

   <script type="text/javascript" src="grained.js"></script>
   <script type="text/javascript" src="index.js"></script>
   </body>
</html>

希望这会有所帮助！如果您有任何疑问，请询问！我愿意提供帮助：D。