// race的原理

Promise.race = function(values){

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

        for(let i = 0 ; i< values.length;i++){

            let current = values[i];

            if((typeof current === 'object' &&  current !==null)|| typeof current == 'function'){

                let then = current.then;

                if(typeof then == 'function'){ // 比较哪个promise比较快，谁快用快

                    then.call(current,resolve,reject)

                }else{

                    resolve(current);

                }

            }else{

                resolve(current);

            }

        }

    });

}