this.setState is not a function 错误仍然存在，即使我遵循了许多使用相同代码的示例

Question

I am new to React, and am trying to fill my components state with data stored on my mongodb Database.

I am using this call to fetch my data:

class DisplayPrograms extends Component {
  constructor(props) {
    super(props);
    this.setState = { programs: [] };
  }

  componentDidMount() {
    axios
      .get("http://localhost:5000/programs")
      .then((response) => {
        console.log(response.data);
        this.setState({ programs: response.data });
      })
      .catch(function (error) {
        console.log(error);
      });
  }

render() { .....

My render() function (not included) is working, and my console.log(response.data) outputs an array of objects like it is supposed to as you can see below, but I keep getting the following error:

Array [ {…}, {…} ]
DisplayProducts.jsx:15
_________________________________________________

TypeError: "this.setState is not a function"
    componentDidMount DisplayProducts.jsx:16
DisplayProducts.jsx:19

I'm sure it's a quick fix but I haven't been able to find a solution.

Answer 1

Your constructor should look like this:

  constructor(props) {
    super(props);
    this.state = { programs: [] };
  }

You were using this.setState() in the constructor instead of this.state Here are the docs on this which show the syntax.

Answer 2

In constructor you need to create the initial state, so you need something like:

constructor(props) {
  super(props);
  this.state = {
    programs: []
  }
}

The this.setState function you can use anywhere else.