Friendly error messages for syntax errors

[shiffman]

In class today when writing objects and constructor functions, the console would not show a syntax error, but rather show a "no p5" error instead. This came up even with some small things like a missing comma or a + instead of = etc. Unfortunately I wasn't able to track all of them, but there is one that produces the problem. The JS error would be undefined is not a function.

var test = {
  x: 200,
  y: 200,
  show: function() {
    ellipse(this.x, this.y, 100, 100);
  }
}

function setup() {
  createCanvas(400, 400);
}

function draw() {
  background(0);
  test.sho();    // ERROR IS HERE!
}

[therewasaguy]

"no p5" happens here at the moment the sketch loads, if an error occurs within a function like draw or setup that is triggered by p5 itself.

Instead of saying "no p5" which is not very helpful, we can see what caused the error and provide a more useful error message.

[therewasaguy]

Now it throws a proper error message

118be84#diff-bdf2da6adcfb8d4a4d7a170c700937d3

...but the line number is off and the message could be friendlier.

[therewasaguy]

We should be printing the second item in the Error stack trace. We could use error.stack but that is not going to work across all browsers. This library may help:

https://github.com/stacktracejs/stacktrace.js