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JavaScript jQuery Basics (2014) Creating a Simple Drawing Application Perform: Part 5

Riccardo Busin
Riccardo Busin
11,741 Points
Posted by Riccardo Busin
Riccardo Busin
11,741 Points

Can't uderstand what's the problem

Hi, i got the "error: app.js:2 Uncaught TypeError: Cannot read property '0' of undefined at app.js:2" and i have no idea why i got it, here's my code and thanks for the time.

var color= $(".selected").css("background-color");
var context = $canvas[0].getContext('2d');
var $canvas = $("canvas")
var lastEvent 



function changeColor() {
  var r = $("#red").val();
  var g = $("#green").val();
  var b = $("#blue").val();
  $("#newColor").css("background-color", "rgb(" + r + "," + g + "," + b + ")");
}



$(".controls").on("click","li", function() {
  $(this).siblings().removeClass("selected");
  $(this).addClass("selected");
  color= $(this).css("background-color");
});

$("#revealColorSelect").click(function() {
  changeColor()
  $("#colorSelect").toggle();
});

$("input[type=range]").change(changeColor);

$("#addNewColor").click(function() {
  var $newColor = $("<li></li>");
  $newColor.css("background-color",$("#newColor").css("background-color"));
  $(".controls ul").append($newColor);
  $newColor.click();
});

$canvas.mousedown(function(e) {
  lastEvent = e;
}).mousemove(function(e){
  context.beginPath();
  context.moveTo(lastEvent.offsetX, lastEvent.offsetY);
  context.lineTo(e.offsetX, e.offsetY);
  context.stroke();
  lastEvent = e;
});

1 Answer

Jason Anello
Jason Anello
Courses Plus Student 94,610 Points

Hi Riccardo,

You have the order of the following 2 lines wrong:

var context = $canvas[0].getContext('2d');
var $canvas = $("canvas")

You first have to assign the canvas element to the $canvas variable and then you can use it to get the context.