React + Fetch+ Json. TypeError: Cannot read property of undefined

Question

当我使用 SuperAgent 时我没有遇到这个问题，但是我决定使用 Window.fetch polifyl 并且我遇到了这个问题。我看到所有数据都已加载，但仍然显示错误。你能帮我找出这个错误吗：

在 render() 中，我根据获得的列表生成了一个组件列表：

    render() {

    if (this.state.data.list) {
        console.log("render: " + this.state.data.list);
        var counter = 0;
        const list = this.state.data.list.map((item) => {
....

Answer 1

您的屏幕截图中的承诺处理程序将不起作用：

.then((json) => console.log('parsed json: ', json))
.then((json) => { this.setState({ data: json }); })

"Take the value from resolving this promise and pass it to console.log. Then, take console.log's return value (which is undefined) and pass it to this.setState."

Answer 2

    fetch(url, {
        headers: {
            'Accept': 'application/json',
        },
    }).then((response) => response.json()
        .catch(err => {
            console.err(`'${err}' happened!`);
            return {};
        }))
        .then((json) => {
            console.log('parsed json: ', json);
            this.setState({ data: json })
        })
        .catch((err) => { console.log('fetch request failed: ', err) }
        )

React + Fetch+ Json. TypeError: Cannot read property of undefined

React + Fetch+ Json. TypeError: Cannot read property of undefined

json

typeerror

fetch

promise

reactjs