Promise.race 的原理

// 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);
            }
        }
    });
}