Promise理解

function a() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            let num = Math.floor(Math.random()*10)
            console.log("[a随机生成num的值]" + num)
            if(num > 5) {
                resolve("成功")
            }else{
                reject("失败")
            }
        }, 1000)

    })
}

function b() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            let num = Math.floor(Math.random()*10)
            console.log("[b随机生成num的值]" + num)
            if(num > 5) {
                resolve("成功")
            }else{
                reject("失败")
            }
        }, 1000)

    })
}

function c() {
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            let num = Math.floor(Math.random()*10)
            console.log("[c随机生成num的值]" + num)
            if(num > 5) {
                resolve("成功")
            }else{
                reject("失败")
            }
        }, 1000)

    })
}

Promise.all([a(), b(), c()]).then(data => {
    console.log(data)
    console.log("a,b,c请求返回成功...执行这里之后操作")
}).catch(error => {
    console.log(error)
    console.log("a,b,c只要其中一个返回失败，最终进入到catch...")
})