(function() {  var Waterfall = function(opts) {    var minBoxWidth;    Object.defineProperty(this, 'minBoxWidth', {      get: function() { return minBoxWidth; },      set: function(value) {        if(value < 100) value = 100;        if(value > 1000) value = 1000;                 minBoxWidth = value;      }    });     opts = opts || {};    var containerSelector = opts.containerSelector || '.wf-container';    var boxSelector = opts.boxSelector || '.wf-box';     // init properties    this.minBoxWidth = opts.minBoxWidth || 250;    this.columns = [];    this.container = document.querySelector(containerSelector);    this.boxes = this.container ?       Array.prototype.slice.call(this.container.querySelectorAll(boxSelector)) : [];     // compose once in constructor    this.compose();     // handle the image or something which might change size after loaded    var images = this.container.querySelectorAll('img'), that = this;    var clr;    for (var i = 0; i < images.length; i++) {      var img = images[i];      img.onload = function() {        if(clr) clearTimeout(clr);         clr = setTimeout(function() {          that.compose(true);        }, 500);      }    }     window.addEventListener('resize', function() {      that.compose();    });  }   // compute the number of columns under current setting  Waterfall.prototype.computeNumberOfColumns = function() {    var num = Math.floor(this.container.clientWidth / this.minBoxWidth);    num = num || 1; // at least one column     return num;  }   // init enough columns and set the width  Waterfall.prototype.initColumns = function(num) {    if(num > 0) {      // create column div      this.columns = [];      var width = (100 / num) + '%';      while(num--) {        var column = document.createElement('div');        column.className = 'wf-column';        column.style.width = width;        this.columns.push(column);        this.container.appendChild(column);      }    }  }   // get the index of shortest column  Waterfall.prototype.getMinHeightIndex = function() {    if(this.columns && this.columns.length > 0) {      var min = this.columns[0].clientHeight, index = 0;      for (var i = 1; i < this.columns.length; i++) {        var columnElem = this.columns[i];        if(columnElem.clientHeight < min) {          min = columnElem.clientHeight;          index = i;        }      }      return index;    }    else return -1;  }   // compose core  Waterfall.prototype.compose = function(force) {    var num = this.computeNumberOfColumns();    var cols = this.columns.length;         if(force || num != cols) {      // remove old column      for (var i = 0; i < this.columns.length; i++) {        var columnElem = this.columns[i];        columnElem.remove();      }       // init new column      this.initColumns(num);       // compose      for (var i = 0, l = this.boxes.length; i < l; i++) {        var box = this.boxes[i];        this.addBox(box);      }    }  }   // add a new box to grid  Waterfall.prototype.addBox = function(elem) {    // push if new box    if(this.boxes.indexOf(elem) < 0) this.boxes.push(elem);     var columnIndex = this.getMinHeightIndex();    if(columnIndex > -1) {      var column = this.columns[columnIndex];      column.appendChild(elem);    }  }   window.Waterfall = Waterfall;})()