Skip to main content

Javascript

Type .js in the first line of an input cell

Try evaluating:

cell
.js
return 1 + 1;

or

.js
const dom = document.createElement('span');
dom.innerText = "Hello World";
dom.style.color = 'lightblue';

return dom;

GitHub repo
JavaScript code is evaluated as a module, which means all defined variables are isolated to the cell.

tip

To define global variables, use the window or core object:

window.variable = 1;

Output Cell​

The return value from the function can be a JavaScript object or a DOM element. DOM elements will be rendered in the output cell.

.js
const canvas = document.createElement('canvas');
const ctx = canvas.getContext('2d');

canvas.width = 500;
canvas.height = 500;

const ballRadius = 10;
let x = canvas.width / 2;
let y = canvas.height - 30;
let dx = 2;
let dy = -2;

function drawBall() {
  ctx.beginPath();
  ctx.arc(x, y, ballRadius, 0, Math.PI * 2);
  ctx.fillStyle = "#0095DD";
  ctx.fill();
  ctx.closePath();
}

let uid;

function draw() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  drawBall();

  if (x + dx > canvas.width - ballRadius || x + dx < ballRadius) {
    dx = -dx;
  }
  if (y + dy > canvas.height - ballRadius || y + dy < ballRadius) {
    dy = -dy;
  }

  x += dx;
  y += dy;

  uid = requestAnimationFrame(draw);
}

uid = requestAnimationFrame(draw);

this.ondestroy = () => {
  cancelAnimationFrame(uid);
};

return canvas;

Context​

There are a few useful built-in objects accessible from within a cell.

this.ondestroy​

This property is called when a cell is destroyed. Assign a clean-up function to it:

this.ondestroy = () => {
  // Clean up resources
};
danger

Always clean up any timers or animation loops using the this.ondestroy property. Otherwise, they will continue running even after the cell is reevaluated.

requestAnimationFrame​

This is a commonly used JavaScript method to sync with the browser’s framerate and render graphics smoothly.

danger

Don’t forget to cancelAnimationFrame using the this.ondestroy method.

Communication with the Wolfram Kernel​

You can define any function for the WLJS interpreter using JavaScript cells. Please refer to these guides:

Also see:

Last updated on