<button onclick="click_promise();">點擊</button>

    <script>
        function use_promise(){
            console.log('方法已經被調用')
            var P = new Promise((resolve,reject)=>{
                setTimeout(()=>{
                    var num = Math.ceil(Math.random()*10)
                    console.log('執行了promise',num)
                    if(num>5){
                        resolve('這是成功后返回的值')
                    }else {
                        reject('這是錯誤后返回的值')
                    }
                },2000)
            })
            return P
        }

        function click_promise(){
            use_promise().then((res)=>{    
                console.log(res)
            })
            .catch((res)=>{
                console.log(res)
            })
        }
    </script>