Question

I have to draw a graph with 3 different lines. A line graph.

I tried doing this:

function draw() 
{  
    var canvas = document.getElementById("canvas");  
    var ctx = canvas.getContext("2d");      
    ctx.lineWidth=10;

    ctx.strokeStyle="teal";
    ctx.moveTo(10,CompanyA[0]);
    ctx.lineTo(110,CompanyA[1]);
    ctx.lineTo(210,CompanyA[2]);
    ctx.stroke();


    ctx.strokeStyle="green";
    ctx.moveTo(10,CompanyB[0]);
    ctx.lineTo(110,CompanyB[1]);
    ctx.lineTo(210,CompanyB[2]);
    ctx.stroke();       

    ctx.strokeStyle="yellow";
    ctx.moveTo(10,CompanyC[0]);
    ctx.lineTo(110,CompanyC[1]);
    ctx.lineTo(210,CompanyC[2]);
    ctx.stroke();
}

But apparently, the last stroke draws for all the lines. So I get 3 yellow lines, instead of a Teal, a Green and a Yellow one.
I tried creating three different Context (ctx1, ctx2 and ctx3), but for some reason, all were drawn with the “ctx3.stroke()” call.

What would be the correct way to do this?

Answer 1

Add a ctx.beginPath() call before every line, and also a ctx.closePath() after every ctx.stroke()

If you don’t, every time you call the stroke() method, not only the new line will be drawn but also all the previous lines will be drawn again (with the new strokeStyle), since it’s the same line path that is still open.