Fine-grained control of randomly entering and exiting things in D3.js, for impeccable object constancy. Adapted from an example co-authored with Mike Bostock.
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <script src="http://d3js.org/d3.v3.min.js"></script> | |
| <style> | |
| html, body { | |
| width: 100%; | |
| height: 100%; | |
| overflow: hidden; | |
| margin: 0; | |
| padding: 0; | |
| } | |
| circle { | |
| fill: black; | |
| stroke: none; | |
| } | |
| circle.saved { | |
| fill: green; | |
| } | |
| </style> | |
| </head> | |
| <body> | |
| <script> | |
| var w = 900, | |
| h = 500, | |
| svg = d3.select('body').append('svg') | |
| .attr('width',w) | |
| .attr('height',h); | |
| var data = [], | |
| removed = []; | |
| function render() { | |
| var circles = svg.selectAll('circle') | |
| .data(data, function(d){ | |
| return d.id; | |
| }); | |
| // the enter() selection needs representation: | |
| circles.enter().append('circle') | |
| .classed('entering',true) | |
| .attr('cx',function(d){ return d.center.x; }) | |
| .attr('cy',function(d){ return d.center.y; }) | |
| .attr('r',100) | |
| .style('opacity',1e-6); | |
| // the exit() selection needs removing | |
| circles.exit().filter(':not(.exiting)') // but only if we didn't already | |
| .classed('exiting',true) | |
| .transition().duration(1000) | |
| .attr('r',100) | |
| .style('opacity',1e-6) | |
| .remove(); | |
| // just for debugging this demo, show which things were saved | |
| // circles.classed('saved',function(d){ return d.saved; }); | |
| // two things here: | |
| // - if something is currently exiting (but in this selection), | |
| // we should cancel its exiting transition and restore it | |
| // - if something is currently entering (it was *just* added), | |
| // we need to trigger a brand new transition | |
| circles.filter('.exiting, .entering') | |
| .classed('exiting',false) | |
| .classed('entering',false) | |
| .transition().duration(1000) | |
| .attr('r',function(d){ return d.radius; }) | |
| .style('opacity',1.0); | |
| console.log(data.length) | |
| } | |
| setInterval(function(){ | |
| // remove a random element ever other tick (or so) | |
| if (data.length > 20 && Math.random() > 0.5) { | |
| var index = Math.floor(Math.random() * data.length); | |
| var item = data[index]; | |
| data.splice(index,1); | |
| // save 1 in 4 removed thing for later restoration | |
| if (Math.random() < 0.25) { | |
| item.saved = true; | |
| removed.push(item); | |
| } | |
| } else { | |
| // if we have something to save, save it: | |
| if (removed.length) { | |
| data.push(removed.pop()); | |
| } else { | |
| // otherwise create a new one | |
| data.push({ | |
| id: new Date().getTime(), | |
| center: { | |
| x: Math.random() * w, | |
| y: Math.random() * h | |
| }, | |
| radius: 2 + Math.random() * 10 | |
| }); | |
| } | |
| } | |
| render(); | |
| }, 30); | |
| </script> |
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