javascript - 从 setTimeout 返回一个值

Question

我正在尝试返回在 setTimout 中计算的值。但似乎我无法获得这个值。我读到要做到这一点我必须使用 promise 。我是否有义务像这样使用这个例子:https://italonascimento.github.io/applying-a-timeout-to-your-promises/ ？

我的代码:

renderTeaserBackground = () => {
    return setTimeout(function() {
        this.setState({ teaserAnimCount: this.state.teaserAnimCount + 1 });
        let teaserBackground = teaserBgImg[this.state.teaserAnimCount];
        console.log(teaserBackground);
    }.bind(this), this.state.teaserAnimDuration * 1000);
    return 'teaserBackground';
}

谢谢

Answer 1

您可以使用 Promise!

ES6 方式 - 标准 promise :

renderTeaserBackground = () => new Promise(res => {
    setTimeout(_ => {
        this.setState({teaserAnimCount: this.state.teaserAnimCount + 1});
        let teaserBackground = teaserBgImg[this.state.teaserAnimCount]
        res(teaserBackground) //Return it here!
    }, this.state.teaserAnimDuration * 1000);
})

要在外部使用它，您可以执行以下操作:

const mainLogic = _ => {
    return renderTeaserBackground().then(teaserBackground => {
        /* Use teaserBackground as you need! */
    })
}

ES7 方式 - Harmony async/await

const mainLogic = async _ => {
    const teaserBackground = await renderTeaserBackground()
    /* Use teaserBackground as you need! */
}