index.js

/**
 * Module dependencies.
 */

var autoscale = require('autoscale-canvas');

/**
 * Expose `Progress`.
 */

module.exports = Progress;

/**
 * Initialize a new `Progress` indicator.
 */

function Progress() {
  this.percent = 0;
  this.el = document.createElement('canvas');
  this.ctx = this.el.getContext('2d');
  this.size(50);
  this.fontSize(11);
  this.font('helvetica, arial, sans-serif');
}

/**
 * Set progress size to `n`.
 *
 * @param {Number} n
 * @return {Progress}
 * @api public
 */

Progress.prototype.size = function(n){
  this.el.width = n;
  this.el.height = n;
  autoscale(this.el);
  return this;
};

/**
 * Set text to `str`.
 *
 * @param {String} str
 * @return {Progress}
 * @api public
 */

Progress.prototype.text = function(str){
  this._text = str;
  return this;
};

/**
 * Set font size to `n`.
 *
 * @param {Number} n
 * @return {Progress}
 * @api public
 */

Progress.prototype.fontSize = function(n){
  this._fontSize = n;
  return this;
};

/**
 * Set font `family`.
 *
 * @param {String} family
 * @return {Progress}
 * @api public
 */

Progress.prototype.font = function(family){
  this._font = family;
  return this;
};

/**
 * Update percentage to `n`.
 *
 * @param {Number} n
 * @return {Progress}
 * @api public
 */

Progress.prototype.update = function(n){
  this.percent = n;
  this.draw(this.ctx);
  return this;
};

/**
 * Draw on `ctx`.
 *
 * @param {CanvasRenderingContext2d} ctx
 * @return {Progress}
 * @api private
 */

Progress.prototype.draw = function(ctx){
  var percent = Math.min(this.percent, 100)
    , ratio = window.devicePixelRatio || 1
    , size = this.el.width / ratio
    , half = size / 2
    , x = half
    , y = half
    , rad = half - 1
    , fontSize = this._fontSize;

  ctx.font = fontSize + 'px ' + this._font;

  var angle = Math.PI * 2 * (percent / 100);
  ctx.clearRect(0, 0, size, size);

  // outer circle
  ctx.strokeStyle = '#9f9f9f';
  ctx.beginPath();
  ctx.arc(x, y, rad, 0, angle, false);
  ctx.stroke();

  // inner circle
  ctx.strokeStyle = '#eee';
  ctx.beginPath();
  ctx.arc(x, y, rad - 1, 0, angle, true);
  ctx.stroke();

  // text
  var text = this._text || (percent | 0) + '%'
    , w = ctx.measureText(text).width;

  ctx.fillText(
      text
    , x - w / 2 + 1
    , y + fontSize / 2 - 1);

  return this;
};