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Editorial Team
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Asked: 2026-05-28T04:36:47+00:00

So what I’m trying to do here is to pass information from a input

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So what I’m trying to do here is to pass information from a input form of number type to javascript and then re-draw the canvas with the updated variable data.

Here’s what I’ve got so far:

<!DOCTYPE HTML>
<html>
<head>
<script language = "JavaScript">

var canvas;
var context;
var _x = 0;

function draw(newx) {
context.rect(newx,100,100,100)
context.strokeStyle = "red"
context.stroke()
}

function sendVal(form) { 
_x = form.xx.value;
context.clearRect(0,0,canvas.width,canvas.height);
draw(_x);
}

window.onload = function() {
canvas = document.getElementById("myCanvas");
context = canvas.getContext("2d");
context.rect(_x,100,100,100);
context.strokeStyle = "blue";
context.stroke();
};

</script>

</head>

<body>

<FORM NAME="SENDX" ACTION="" METHOD="GET">
Enter X: <INPUT TYPE="number" NAME="xx">
<INPUT TYPE="submit" VALUE="ENTER CO-ORDINATES" onClick="sendVal(this.form)">
</FORM>

<canvas id="myCanvas" width="500" height="500"></canvas>

</body>
</html>

As you can see above, I’ve tried making the canvas’s context variable public so that I can access its functions from another part of the javascript, but the canvas never updates itself. How do I fix this? Thanks.

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1 Answer

  1. Editorial Team

    I think your problem is not in the JavaScript but the HTML, an input of type “submit” wants to cause a form submit event, you just want an onclick event. Try just using:

    <input type="button" value="ENTER CO-ORDINATES" onclick="sendVal(this.form)">

    Working JSFiddle: http://jsfiddle.net/nwellcome/mJyps/5/

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