Javascript 如何从json中选择特定值？

我想得到的是选择“medium-mp4”的“url”值

组件

componentDidMount() { return fetch('https://you-link.herokuapp.com') .then((response) => response.json()) .then((responseJson) => { this.setState({ isLoading: false, dataSource: responseJson, videoUrl: responseJson[0].url }, function() { }); }) .catch((error) => { console.error(error); }); } componentDidMount（）{ 返回获取（'https://you-link.herokuapp.com') .then（（response）=>response.json（）） .然后（（responseJson）=>{ 这是我的国家({ 孤岛加载：false， 数据来源：responseJson， videoUrl:responseJson[0]。url }，函数（）{ }); }) .catch（（错误）=>{ 控制台错误（error）； }); } Json调用

---

响应不是数组，而是对象，因此不能使用0。请尝试使用所需的对象键

{
  videoUrl: responseJson['hd720-mp4'].url
}

您可以使用上面的命令获取url值。

试试这个代码片段

videoUrl: responseJson['medium-mp4'].url

---

videoUrl:responseJson[“medium-mp4”]。url

你试过

responseJson[0]['medium-mp4']吗。url

？我试过了，但不起作用。然后（（response）=>response.json（）。然后(（responseJson）=>{let url=responseJson.find（obj=>obj.responseJson['hd720-mp4']）.url this.setState（{isLoading:false，dataSource:responseJson，videoUrl:url}，function（）{}）；catch（（error）=>{console.error（error）；}）}你检查为“正确答案”，和我告诉你的一样，哈哈

                let objMusic = JSON.parse('{"hd720-mp4":{"itag":"22","quality":"hd720","type":"video/mp4","url":"https://r5---sn-5uaezn6y.googlevideo.com/videoplayback?mn=sn-5uaezn6y,sn-q4flrnl7&mm=31,26&id=o-AID9zwFrzXB9sFZjRYPFuJyVV_ViYTpwz40-0Po2qR-P&c=WEB&mime=video/mp4&lmt=1537717779316991&ip=2a02:4780:1:3::f&pl=48&itag=22&dur=295.706&mv=u&source=youtube&ms=au,onr&fvip=5&ei=sKPzW-6XIZCPj-8PzruZ-A4&requiressl=yes&sparams=dur,ei,id,ip,ipbits,itag,lmt,mime,mm,mn,ms,mv,pl,ratebypass,requiressl,source,expire&mt=1542693264&expire=1542715408&ipbits=0&key=yt6&signature=B59110AC6E15FAE514C4B18679750702C9069E83.B0AC77A3AEBC7EC3CE20D218C67E8AE80E745E8A&ratebypass=yes&signature="},"medium-webm":{"itag":"43","quality":"medium","type":"video/webm","url":"https://r5---sn-5uaezn6y.googlevideo.com/videoplayback?mn=sn-5uaezn6y,sn-q4flrnl7&mm=31,26&id=o-AID9zwFrzXB9sFZjRYPFuJyVV_ViYTpwz40-0Po2qR-P&lmt=1540750584717310&ip=2a02:4780:1:3::f&pl=48&dur=0.000&mv=u&source=youtube&ms=au,onr&ei=sKPzW-6XIZCPj-8PzruZ-A4&sparams=clen,dur,ei,gir,id,ip,ipbits,itag,lmt,mime,mm,mn,ms,mv,pl,ratebypass,requiressl,source,expire&mt=1542693264&expire=1542715408&txp=5511222&key=yt6&gir=yes&ipbits=0&c=WEB&mime=video/webm&itag=43&fvip=5&ratebypass=yes&requiressl=yes&clen=30067021&signature=238FF11CC09F405CFD24423203F813EDFB5D66C2.3003162315BC1FF6A5D0C3B19BB03F9E1016E780&signature="},"medium-mp4":{"itag":"18","quality":"medium","type":"video/mp4","url":"https://r5---sn-5uaezn6y.googlevideo.com/videoplayback?mn=sn-5uaezn6y,sn-q4flrnl7&mm=31,26&id=o-AID9zwFrzXB9sFZjRYPFuJyVV_ViYTpwz40-0Po2qR-P&lmt=1537716294977165&ip=2a02:4780:1:3::f&pl=48&dur=295.706&mv=u&source=youtube&ms=au,onr&ei=sKPzW-6XIZCPj-8PzruZ-A4&sparams=clen,dur,ei,gir,id,ip,ipbits,itag,lmt,mime,mm,mn,ms,mv,pl,ratebypass,requiressl,source,expire&mt=1542693264&expire=1542715408&key=yt6&gir=yes&ipbits=0&c=WEB&mime=video/mp4&itag=18&fvip=5&ratebypass=yes&requiressl=yes&clen=23503941&signature=DA800A9574CBF4EA8666390C6F98562A70EBE3EE.9C3BD58181B597C780E5264498B0919D2B0B8453&signature="},"small-3gpp":{"itag":"17","quality":"small","type":"video/3gpp","url":"https://r5---sn-5uaezn6y.googlevideo.com/videoplayback?mn=sn-5uaezn6y,sn-q4flrnl7&mm=31,26&txp=5531232&id=o-AID9zwFrzXB9sFZjRYPFuJyVV_ViYTpwz40-0Po2qR-P&c=WEB&sparams=clen,dur,ei,gir,id,ip,ipbits,itag,lmt,mime,mm,mn,ms,mv,pl,requiressl,source,expire&mime=video/3gpp&lmt=1540636712468197&ip=2a02:4780:1:3::f&pl=48&itag=17&dur=295.729&mv=u&source=youtube&ms=au,onr&fvip=5&ei=sKPzW-6XIZCPj-8PzruZ-A4&requiressl=yes&clen=2800636&mt=1542693264&expire=1542715408&ipbits=0&key=yt6&signature=4E618E1E6289DAC12A897896C9D2DEDA304DB55D.2240D0C7E9911C62537A948D6795EF7E171AA7CC&gir=yes&signature="}}')
                if (objMusic['medium-mp4']) {
                    let mp4 = objMusic['medium-mp4']
                    let url = mp4.url
                    alert(JSON.stringify(url))
                }

videoUrl: responseJson['medium-mp4'].url