返回setTimeout[duplicate]中的值

Question

我正在尝试返回在setTimout中计算的值。但好像我拿不出这个值。我读到要做到这一点，我必须用promise。我是否必须像下面这样使用它：https://italonascimento.github.io/application-a-timeout-to-your-promissions/？

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';
}

Answer 1

你可以用一个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);
})

若要在外部使用此功能，您可以执行以下操作：

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

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