promise关键问题
作者：互联网
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Promise关键问题 - Promise 对象状态改变的方式</title>
</head>
<body>
<script>
let p = new Promise((resolve, reject) => {
//三种方法：
//1. resolve 函数
// resolve('ok'); // pending => fulfilled (resolved)
//2. reject 函数
// reject("error");// pending => rejected
//3. 抛出错误
// throw '出问题了';
});
console.log(p);
</script>
</body>
</html>
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<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Promise关键问题 - Promise 指定多个回调</title>
</head>
<body>
<script>
let p = new Promise((resolve, reject) => {
// resolve('OK');
});
///指定回调 - 1
p.then(value => {
console.log(value);
});
//指定回调 - 2
p.then(value => {
alert(value);
});
</script>
</body>
</html>
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<html lang="en">
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<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Promise关键问题 - Promise 改变状态与指定回调的顺序问题</title>
</head>
<body>
<script>
let p = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('OK');
}, 1000);
});
p.then(value => {
console.log(value);
},reason=>{
})
</script>
</body>
</html>
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<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Promise关键问题 - Promise then方法的返回结果特点</title>
</head>
<body>
<script>
let p = new Promise((resolve, reject) => {
resolve('ok');
});
//执行 then 方法
let result = p.then(value => {
// console.log(value);
//1. 抛出错误
// throw '出了问题';
//2. 返回结果是非 Promise 类型的对象
// return 521;
//3. 返回结果是 Promise 对象
// return new Promise((resolve, reject) => {
// // resolve('success');
// reject('error');
// });
}, reason => {
console.warn(reason);
});
console.log(result);
</script>
</body>
</html>
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<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Promise关键问题 - 如何串联多个任务</title>
</head>
<body>
<script>
let p = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('OK');
}, 1000);
});
p.then(value => {
return new Promise((resolve, reject) => {
resolve("success");
});
}).then(value => {
console.log(value);
}).then(value => {
console.log(value);
})
</script>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Promise关键问题 - 异常穿透</title>
</head>
<body>
<script>
let p = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('OK');
// reject('Err');
}, 1000);
});
p.then(value => {
// console.log(111);
throw '失败啦!';
}).then(value => {
console.log(222);
}).then(value => {
console.log(333);
}).catch(reason => {
console.warn(reason);
});
</script>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Promise关键问题 - 中断 Promise 链条</title>
</head>
<body>
<script>
let p = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('OK');
}, 1000);
});
p.then(value => {
console.log(111);
//有且只有一个方式
return new Promise(() => {});
}).then(value => {
console.log(222);
}).then(value => {
console.log(333);
}).catch(reason => {
console.warn(reason);
});
</script>
</body>
</html>
标签：resolve,console,log,value,Promise,reject,promise,关键问题 来源： https://www.cnblogs.com/juham/p/14906350.html