gsap, react - Cannot tween a null target

Question

Following this tutorial I am trying to implement a similar component using typescript.

My Component:

import React, { Component } from "react";
import TransitionGroup from "react-addons-transition-group";
import { TweenMax } from "gsap";

import { tableOfContentsData } from "../mockData/tableOfContents";
import { Chapter } from "../types/data/tableOfContents";

import styled from "styled-components";
import { pallete } from "../constants/pallete";

type State = {
  isExpanded: boolean;
};

const StyledContainer = styled.div`
  position: fixed;
  top: 0;
  left: 0;
  padding: 1em;
  background-color: ${pallete.primary};
  color: ${pallete.text};
  font-size: 16px;
  height: 100vh;
  max-width: 200px;
  .chapter-link {
    min-height: 24px;
    min-width: 54px;
    margin-bottom: 1em;
  }
  .close-btn {
    background-color: ${pallete.secondary};
    position: absolute;
    top: 0;
    right: -54px;
    height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    width: 54px;
  }
`;

class TableOfContents extends Component<{}, State> {
  state = {
    isExpanded: true
  };

  toggleExpanded = (): void => {
    this.setState({
      isExpanded: !this.state.isExpanded
    });
  };

  render() {
    return (
      <StyledContainer>
        <TransitionGroup>
          {this.state.isExpanded && <ChaptersList />}
        </TransitionGroup>
        <div className="close-btn" onClick={this.toggleExpanded}>
          &lt;
        </div>
      </StyledContainer>
    );
  }
}

class ChaptersList extends Component {
  componentWillEnter(callback: any) {
    const el = (this as any).container;
    TweenMax.fromTo(
      el,
      0.3,
      { x: -100, opacity: 0 },
      { x: 0, opacity: 1, onComplete: callback }
    );
  }

  componentWillLeave(callback: any) {
    const el = (this as any).container;
    TweenMax.fromTo(
      el,
      0.3,
      { x: 0, opacity: 1 },
      { x: -100, opacity: 0, onComplete: callback }
    );
  }

  render() {
    return (
      <div>
        {tableOfContentsData.map((chapter: Chapter, i: number) => (
          <div key={i} className="chapter-link">
            {chapter.title}
          </div>
        ))}
      </div>
    );
  }
}

export default TableOfContents;

When I click the .close-btn div I get the following error:

uncaught exception: Cannot tween a null target.

One of the possible errors I found during googling is the TweenMax import, but if I try to import it from gsap/TweenMax, ts complains about missing type definitions (I have @types/gsap installed).

Answer 1

You aren't currently doing anything in ChaptersList to set this.container, so el will be undefined. This should be handled via a ref on the outermost div.

The render of ChaptersList should look like:

render() {
    return (
      <div ref={c => (this as any).container = c}>{/* this is the change */}
        {tableOfContentsData.map((chapter: Chapter, i: number) => (
          <div key={i} className="chapter-link">
            {chapter.title}
          </div>
        ))}
      </div>
    );
  }