1

我需要在 jQuery 插件中为响应式视差背景图像及其位置实现多 if...else if...else 语句。

我到目前为止的代码是：

if ($thirdBG.hasClass("inview")){
  //call the newPos function and change the background position
  $thirdBG.css({'backgroundPosition': newPos(0, windowHeight, pos, 2550, 0)});
  //$secondBG.css({'backgroundPosition': newPos(50, windowHeight, pos, 1550, 0.3)});
  if (current_width < 960) {
    bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 6350, 0.2)});
  }
  else if (current_width < 768) {
    bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 6350, 0.2)});
  }
  else if (current_width < 480) {
    bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 6350, 0.2)});
  }
  else if (current_width < 320) {
    bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 6350, 0.2)});
  }
  else {
    bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 4910, 0.2)});
  }
  //bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 4910, 0.2)});
  //call the newPos function and change the second background position
}

然而，这并不是我想要的。此代码定义宽度是否小于某个大小。我希望它说类似

if (current_width > 320 and < 480) {
  bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 6350, 0.2)});
}

我想要的基本上是：

在位置 X 显示 bg3 以获取以下尺寸范围：

大于 320 小于等于 480 大于 480 小于等于 768 大于 768 小于等于 960 大于 960

不确定语法需要是什么。

有没有比我拥有的多个 if...else if...else 语句更有效的方法来编写该代码？

最后，我想知道如何在屏幕上回显当前的垂直滚动位置，这样我就可以知道图像的位置，而无需保存和重新加载页面 1000 次。

在此处添加完整的 nbw-parallax.js 插件代码：

/*
Demo: Despiration Tutorial Parallax Demo
Author: Elias Ghosn - Despiration.com
Author URL: http://www.despiration.com/
Tutorial URL: http://www.ianlunn.co.uk/blog/code-tutorials/recreate-nikebetterworld-parallax/

License: http://creativecommons.org/licenses/by-sa/3.0/ (Attribution Share Alike). Please attribute work to Despiration.com simply by leaving these comments in the source code or if you'd prefer, place a link on your website to http://www.despiration.com/.

Dual licensed under the MIT and GPL licenses:
http://www.opensource.org/licenses/mit-license.php
http://www.gnu.org/licenses/gpl.html
*/

$(document).ready(function() { //when the document is ready...
    var current_width = $(window).width();
     //do something with the width value here!
     //jQuery('nav').removeClass("is-sticky");
    if(current_width < 960){
      jQuery('nav').addClass("is-sticky");

    }
    $(".menusel").click(function () {   $(".mobico").fadeIn('slow');});
    $(".mobico a").click(function () {   $(".mobico").fadeOut('slow');});
    //save selectors as variables to increase performance
    var $window = $(window);
    var $firstBG = $('#intro');
    var bg1 = $("#intro .bg1");
    var $secondBG = $('#separator1');
    var bg2 = $("#separator1 .bg2");
    var $thirdBG = $('#separator2');
    var bg3 = $("#separator2 .bg3");
    var $fourthBG = $('#separator3');
    var bg4 = $("#separator3 .bg4");

    var windowHeight = $window.height(); //get the height of the window


    //apply the class "inview" to a section that is in the viewport
    $('#intro, #separator1, #separator2, #separator3').bind('inview', function (event, visible) {
            if (visible == true) {
            $(this).addClass("inview");
            } else {
            $(this).removeClass("inview");
            }
        });


    //function that places the navigation in the center of the window
    function RepositionNav(){
        var windowHeight = $window.height(); //get the height of the window
        var navHeight = $('#nav').height() / 2;
        var windowCenter = (windowHeight / 2);
        var newtop = windowCenter - navHeight;
        $('#nav').css({"top": newtop}); //set the new top position of the navigation list
    }

    //function that is called for every pixel the user scrolls. Determines the position of the background
    /*arguments:
        x = horizontal position of background
        windowHeight = height of the viewport
        pos = position of the scrollbar
        adjuster = adjust the position of the background
        inertia = how fast the background moves in relation to scrolling
    */
    function newPos(x, windowHeight, pos, adjuster, inertia){
        return x + "% " + (-((windowHeight + pos) - adjuster) * inertia)  + "px";
    }

    //function to be called whenever the window is scrolled or resized
    function Move(){
        var pos = $window.scrollTop(); //position of the scrollbar

        //if the first section is in view...
        if($firstBG.hasClass("inview")){
            //call the newPos function and change the background position
            $firstBG.css({'backgroundPosition': newPos(0, windowHeight, pos, 500, 0)});
            //call the newPos function and change the second background position
            bg1.css({'backgroundPosition': newPos(50, windowHeight, pos, 0, 0.2)});
        }

        //if the second section is in view...
        if($secondBG.hasClass("inview")){
            //call the newPos function and change the background position
            $secondBG.css({'backgroundPosition': newPos(0, windowHeight, pos, 1550, 0)});
            //$secondBG.css({'backgroundPosition': newPos(50, windowHeight, pos, 1550, 0.3)});
            bg2.css({'backgroundPosition': newPos(90, windowHeight, pos, 2610, 0.2)});
            //call the newPos function and change the second background position
        }

        if ($thirdBG.hasClass("inview")){
            //call the newPos function and change the background position
            $thirdBG.css({'backgroundPosition': newPos(0, windowHeight, pos, 2550, 0)});
            //$secondBG.css({'backgroundPosition': newPos(50, windowHeight, pos, 1550, 0.3)});
            if (current_width < 320) {
                bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 6350, 0.2)});
            }
            else if (current_width = 320 && < 480) {
                bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 6350, 0.2)});
            }
            else if (current_width = 480 && < 768) {
                bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 6350, 0.2)});
            }
            else if (current_width = 768 && < 960) {
                bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 6350, 0.2)});
            }
            else {
                bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 4910, 0.2)});
            }
            //bg3.css({'backgroundPosition': newPos(50, windowHeight, pos, 4910, 0.2)});
            //call the newPos function and change the second background position
        }

        if ($fourthBG.hasClass("inview")){
            //call the newPos function and change the background position
            $fourthBG.css({'backgroundPosition': newPos(0, windowHeight, pos, 5850, 0)});
            //$secondBG.css({'backgroundPosition': newPos(50, windowHeight, pos, 1550, 0.3)});
            //call the newPos function and change the second background position
            if (current_width < 320) {
                bg4.css({'backgroundPosition': newPos(50, windowHeight, pos, 8110, 0.2)});
            }
            else if (current_width = 320 && < 480) {
                bg4.css({'backgroundPosition': newPos(50, windowHeight, pos, 8110, 0.2)});
            }
            else if (current_width = 480 && < 768) {
                bg4.css({'backgroundPosition': newPos(50, windowHeight, pos, 8110, 0.2)});
            }
            else if (current_width = 768 && < 960) {
                bg4.css({'backgroundPosition': newPos(50, windowHeight, pos, 8110, 0.2)});
            }
            else {
                bg4.css({'backgroundPosition': newPos(50, windowHeight, pos, 6110, 0.20)});
            }
        //bg4.css({'backgroundPosition': newPos(50, windowHeight, pos, 6110, 0.20)});
        }

        $('#pixels').html(pos); //display the number of pixels scrolled at the bottom of the page
    }

    RepositionNav(); //Reposition the Navigation to center it in the window when the script loads

    $window.resize(function(){ //if the user resizes the window...
    var current_width = $(window).width();
     //do something with the width value here!
    // jQuery('nav').removeClass("is-sticky");
    if(current_width < 960){
      jQuery('nav').addClass("is-sticky");

    }
        Move(); //move the background images in relation to the movement of the scrollbar
        RepositionNav(); //reposition the navigation list so it remains vertically central
    });

    $window.bind('scroll', function(){ //when the user is scrolling...
        Move(); //move the background images in relation to the movement of the scrollbar
    });

});
4

2 回答 2

2

关于声明的第一件事if：你可以写：

if( width < someval ){
    .
    .
} else if( width > someotherval && width < sometotalotherval ){

} else {

}

所以使用&&or||运算符。

我不知道您所说的“回显并保存 100 次”是什么意思。

问候...

编辑：

为了这个评论片段：

我需要知道的是 div 在浏览器窗口中以不同宽度开始和结束的位置（不仅是前面的 div，还有后面的 bg div。

看看：

<element>.getBoundingClientRect()

方法。它返回四个值：任意 html 元素的顶部、左侧、右侧和底部，它们的原点是屏幕的左上角。因此，如果一个元素不可见，因为它位于顶部并且文档向下滚动，则顶部值为负数，如果底部值也是负数，则您知道该元素完全不可见。使用此方法，您可以轻松获取 div 的开头和结尾。

于 2012-11-22T07:15:38.243 回答
0

如果您首先使用最低值颠倒您的语句顺序，您将不会遇到相同的重叠问题。只有一个条件为真

if( current_width < 320 ){

}else if( current_width < 480){
  /* true when greater or equal to 320 and less than 480 */
}

/* etc*/
于 2012-11-22T07:14:28.770 回答