this.setState((prevState) => {   
    const newArray = [...prevState.array];   
    newArray[index] = updatedValue;   
    return { array: newArray };   
});

this.setState((prevState) => {   
    const newArray = [...prevState.array];   
    newArray[index] = updatedValue;   
    return { array: newArray };   
});

React可以批处理更新，因此正确的方法是为setState提供一个执行更新的函数。

对于React更新插件，以下将可靠地工作:

this.setState( state => update(state, {array: {$push: [4]}}) );

或者对于concat():

this.setState( state => ({
    array: state.array.concat([4])
}));

下面以https://jsbin.com/mofekakuqi/7/edit?js,output为例说明如果您弄错了会发生什么。

setTimeout()调用正确地添加了三个项，因为React不会在setTimeout回调中批量更新(参见https://groups.google.com/d/msg/reactjs/G6pljvpTGX0/0ihYw2zK9dEJ)。

错误onClick只会添加“第三”，但固定的一个，将添加F, S和T如预期。

class List extends React.Component {
  constructor(props) {
    super(props);

    this.state = {
      array: []
    }

    setTimeout(this.addSome, 500);
  }

  addSome = () => {
      this.setState(
        update(this.state, {array: {$push: ["First"]}}));
      this.setState(
        update(this.state, {array: {$push: ["Second"]}}));
      this.setState(
        update(this.state, {array: {$push: ["Third"]}}));
    };

  addSomeFixed = () => {
      this.setState( state => 
        update(state, {array: {$push: ["F"]}}));
      this.setState( state => 
        update(state, {array: {$push: ["S"]}}));
      this.setState( state => 
        update(state, {array: {$push: ["T"]}}));
    };



  render() {

    const list = this.state.array.map((item, i) => {
      return <li key={i}>{item}</li>
    });
       console.log(this.state);

    return (
      <div className='list'>
        <button onClick={this.addSome}>add three</button>
        <button onClick={this.addSomeFixed}>add three (fixed)</button>
        <ul>
        {list}
        </ul>
      </div>
    );
  }
};


ReactDOM.render(<List />, document.getElementById('app'));

//get the value you want to add
const valor1 = event.target.elements.valor1.value;

//add in object 
        const todo = {
            valor1,
        }

//now you just push the new value into the state

//prevlista is the value of the old array before updating, it takes the old array value makes a copy and adds a new value

setValor(prevLista =>{
return prevLista.concat(todo) })
     

这段代码为我工作:

fetch('http://localhost:8080')
  .then(response => response.json())
  .then(json => {
    this.setState({mystate: this.state.mystate.push.apply(this.state.mystate, json)})
  })

ES6最简单的方法:

this.setState(prevState => ({
    array: [...prevState.array, newElement]
}))