How to color every second row using jQuery when the number of element in a row is variable?

Consider the following example which should color every second row: (live demo here)

JS:

$(function() {
    var wrapper = $("<div></div>")

    for (i = 0; i < 100; i++) {
        wrapper.append("<span></span>");
    }

    $("body").append(wrapper);

    color_rows();
});

function color_rows() {
    $("span").each(function(i) {
        if (i % 10 >= 5) {
            $(this).css("background-color", "red");
        }
    });
}

CSS:

div {
    width: 450px;
    heig开发者_开发百科ht: 400px;
    background-color: #ccc;
    overflow: auto;
}
span {
    display: inline-block;
    width: 50px;
    height: 50px;
    background-color: #777;
    margin: 0 30px 30px 0;
}

The output is:

As you can see, color_rows() function assumes that there are 5 elements per row. If, for example, I change the width of the div to be 350px, the color_rows() function will not work properly (i.e. will not color every second row).

How could I fix color_rows() so that it will work for every width of the div ?

---

this is my solution:

this works based on the top offset of each element and by comparing the it to the top offset of last element in the loop it detects if new row is seen or not, and then based on the number of row colors rows.

function color_rows() {
    var lastTop = -1;
    var rowCount = 0;
    $("span").each(function(i) {
        var top = $(this).position().top;
        if (top != lastTop) {
            rowCount++;
            lastTop = top;
        }
        if(rowCount % 2 == 0)
        {
            $(this).css("background-color", "red");
        }
    });
}

jsFiddle: http://jsfiddle.net/Ug6wD/4/

---

Look at my fixes http://jsfiddle.net/Ug6wD/5/

I am getting Container width, itemWidth + margin. And calculating how many items per row. Get margin-right from span item.

Then minus 20 to the container width, coz of overflow scrollbar.

function color_rows() {
var containerWidth = $('div').width()-20;
var itemWidth = $('span:first').width() + parseInt($('span:first').css('margin-right'));
var itemsPerRow = parseInt(containerWidth / itemWidth);

$("span").each(function(i) {
    if (i % (itemsPerRow *2) >= itemsPerRow ) {
        $(this).css("background-color", "red");
    }
});

} UPDATE with dynamic margin-right value from CSS AND Right scrollbar fix causing breakage : http://jsfiddle.net/Ug6wD/5/

---

Edit: This only works on some div-widths.. -.- Nevermind, then..

This should do it:

function color_rows() {
    var divW = $('div').width();
    var spanW = $('span').outerWidth(true);   //Get margin too
    var cnt = parseInt(divW/spanW, 10);   //Remove decimals
    $("span").each(function(i) {
        if (i % (cnt*2) >= cnt) {
            $(this).css("background-color", "red");
        }
    });
}

---

fiddle: http://jsfiddle.net/gn5QW/1/

html

<div id="container">
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
</div>

js

$(document).ready(function(){
    var box = $(".box");
    var con = $("#container");
    var box_per_line = Math.floor(parseInt($("#container").width())/ (parseInt( $(".box").width()) +10*2/*px*/));
    var style = "black";
    $(".box").each(function(i){
        if(i % box_per_line == 0){ style = (style == "black") ? "grey" : "black"; }
        $(this).css("background-color",style);
    });
});

css

.box {
    width: 100px;
    height: 100px;
    float: left;
    margin: 10px;
}

#conainer {
    background-color: grey;
    display: inline-block;
}

---

I've fixed your code, but please PLEASE don't do this. The internet the in pain,

$(function() {
    var wrapper = $("<div></div>")

    for (i = 0; i < 100; i++) {
        wrapper.append("<span></span>");
    }

    $("body").append(wrapper);

    color_rows();
});

function color_rows() {
        var rowWidth = Number( $('div:first').css('width').slice(0,-2) );
        var itemWidth = Number( $('span:first').css('width').slice(0,-2) ) + Number( $('span:first').css('margin-right').slice(0,-2) );
        var perRow =  Math.floor( rowWidth/itemWidth );

    $("span").each(function(i) {
        if (i % 10 >= perRow ) {
            $(this).css("background-color", "red");
        }
    });
}

---

There is a simpler way:

$('tr:even').css("background-color", "red");