typeScript-promise

function add(a:number,b:number) :Promise<number>{

        return new Promise((resolve,reject)=>{

        if(b % 17 === 0){

                reject('bad number')

        }

        setTimeout(()=>{

                resolve(a+b)

        },2000)

        })

}

function mul(a:number,b:number) :Promise<number>{

        return new Promise((resolve,reject)=>{

                setTimeout(()=>{

                        resolve(a*b)

                },2000)

               })

        }

add(2,17).then(res=>{

console.log('2+17',res)

return mul(res,4)

}).then(res=>{

console.log('(2+3)*4',res)

return mul(res,5)

}).then(res=>{

console.log('20*5',res)

}).catch(err=>{

console.log("catch",err)

})

// add(2,3)

// .then(res=>add(res,4))

// .then(res=>add(res,8))

// .then(res=>{

// console.log("redult",res)

// })