ES6箭頭功能和setTimeOut

Question

下面的代碼總是打印相同的隨機數，我在setTimeout中使用let和arrow函數。

 let getRandom = new Promise((resolve, reject) => { setTimeout( () => { let random = parseFloat(Math.random() * 30); if(random > 20) { resolve(`Yes!! ${random} is our random number`); } else { reject(`Oh no!! ${random} is not our random number`); } }, parseInt(Math.random()*1000)); }); for(let counter = 0; counter < 10; counter++) { getRandom.then( response => { console.log(response); }, error => { console.log(error); }); } 

Answer 1

getRandom是一個單一的無極，它創建了一個單一的一個承諾setTimeout並解析（或拒絕）給一個（單個）的字符串。 您需要一個函數來創建一個Promise，以便多次調用該函數將導致創建多個Promises（和多個隨機數）：

 const getRandom = () => new Promise((resolve, reject) => { setTimeout(() => { const random = Math.random() * 30; if (random > 20) { resolve(`Yes!! ${random} is our random number`); } else { reject(`Oh no!! ${random} is not our random number`); } }, Math.random() * 1000); }); for (let counter = 0; counter < 10; counter++) { getRandom() .then(console.log) .catch(console.log); }