How to access canvas context in React

Question

I made a color picker with React and Canvas. Currently the components are rendered in React and canvas is done with vanilla javascript. I'd like to two to mesh more, so I want the click events to be handled with React.

For example, this

colorStrip.addEventListener("click", click, false);

function click(e) {
  x = e.offsetX;
  y = e.offsetY;
  var imageData = context.getImageData(x, y, 1, 1).data;
  rgbaColor = 'rgba(' + imageData[0] + ',' + imageData[1] + ',' + imageData[2] + ',1)';
  fillGradient();
}

I would hope would be able to translate to this

var ColorPicker = React.createClass({
  colorStripClick: function() {
    //handle click events here
  },
  render: function() {
    var styles = {
      opacity: this.props.isVisible ? '1' : '0'
    };
    return(
      <div id="color-picker" style={styles}>
        <canvas id="color-block" height="150" width="150"></canvas>
        <canvas id="color-strip" height="150" width="30" onClick={this.colorStripClick}></canvas>
      </div>
    );
  }
});

But that doesn't work because I don't know how to access context. How can I get access to the canvas properties with React? Is there a way to access it before the click?

UPDATE

I used David's answer but I was getting errors by putting a function in ref so I did ref="canvasBlock" and ref="canvasStrip" instead and then assigned the context in componentDidMount

Answer 1

You can add a ref function attribute on the canvas element:

<canvas id="color-strip" ref={(c) => this.context = c.getContext('2d')} height="...

Then you’ll have access to the context through this.context:

colorStripClick: function() {
    var imageData = this.context.getImageData(x, y, 1, 1).data
}

You can also use the event object to access to DOM node as already pointed out, but this way you’ll have access from anywhere, not just event handlers.