javascript - Chart.js : Controller for Scatter chart doesn't work for draw function -


following link extend scatter type draw() function print "no data found" in center y axis scale.

here's code:

chart.defaults.derivedscatter = chart.defaults.scatter;  var ctx = canvas.getcontext("2d");  var custom = chart.controllers.scatter.extend({     draw: function() {         chart.controllers.scatter.prototype.draw.call(this);          this.chart.chart.ctx.textalign = "center";         this.chart.chart.ctx.font = "11px arial";         this.chart.chart.ctx.filltext("no data found", 45, 100);     } });  chart.controllers.derivedscatter = custom;  chart = new chart(ctx, {     type: "derivedscatter",     options: {         scales: {             yaxes: [{                 ticks: {                     beginatzero:true,                     max:0.10,                     stepsize:0.001,                     callback: function(label, index, labels) {                         var n = parsefloat(label);                         return (math.round(n*1000)/10).tofixed(1);                     }                 },                 gridlines: {                     display: false,                     drawborder: false                 }             }],             xaxes: [{                 display: false,                 gridlines: {                    display: false                 }             }]         },         legend: {             display:false         },         responsive: false     } });

i getting y axis scale don't see no data found text in center of chart. doesn't seem work.

looked @ this , this stack-overflow answers come solution.

note: here doesn't have built in type scatter. reason?

any other approach or other appreciated.

the reason why it­'s not working because, haven't initialized data property of chart. in order use extended dataset controller, must initialize / set data.datasets property while constructing chart, :

... chart = new chart(ctx, {    type: "derivedscatter",    data: {       datasets: [{}]    },    options: { ...

note: important part initialize datasets property , doesn't have contain data.

ᴡᴏʀᴋɪɴɢ ᴇxᴀᴍᴘʟᴇ ⧩

var ctx = canvas.getcontext("2d");    chart.defaults.derivedscatter = chart.defaults.scatter;    var custom = chart.controllers.scatter.extend({     draw: function() {        chart.controllers.scatter.prototype.draw.call(this);          this.chart.chart.ctx.textalign = "center";        this.chart.chart.ctx.font = "11px arial";        this.chart.chart.ctx.filltext("no data found", 80, 80);     }  });    chart.controllers.derivedscatter = custom;    chart = new chart(ctx, {     type: "derivedscatter",     data: {        datasets: [{}]     },     options: {        scales: {           yaxes: [{              ticks: {                 beginatzero: true,                 max: 0.10,                 stepsize: 0.001,                 callback: function(label, index, labels) {                    var n = parsefloat(label);                    return (math.round(n * 1000) / 10).tofixed(1);                 }              },              gridlines: {                 display: false,                 drawborder: false              }           }],           xaxes: [{              display: false,              gridlines: {                 display: false              }           }]        },        legend: {           display: false        },        responsive: false     }  });
<script src="https://cdnjs.cloudflare.com/ajax/libs/chart.js/2.7.0/chart.min.js"></script>  <canvas id="canvas"></canvas>


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