Nodejs异步编程之Promiseschaining

1. 案例一

1.1. 案例描述

resolve()函数的输入参数&＃xff1a;无
用户函数函数的返回值&＃xff1a;无
函数书写形式&＃xff1a;完整
Promise: ×1
chain: ×1

1.2. 源代码 “case1.js”

let promise &＃61; new Promise(function(resolve, reject){console.log(&＃39;Initialize a Promise to Complete Five Things Sequentially 1 -> 2 -> 3 -> 4 -> 5 as follows:&＃39;);resolve();}
);promise.then(function(){console.log("Thing 1");}
).then(function(){console.log("Thing 2");}
).then(function(){console.log("Thing 3");}
).then(function(){console.log("Thing 4");}
).then(function(){console.log("Thing 5");}
)


1.3. 运行结果

$ node case1.js
Initialize a Promise to Complete Five Things Sequentially 1 -> 2 -> 3 -> 4 -> 5 as follows:
Thing 1
Thing 2
Thing 3
Thing 4
Thing 5


2. 案例二

2.1. 案例描述

resolve()函数的输入参数&＃xff1a;无
用户函数函数的返回值&＃xff1a;有
函数书写形式&＃xff1a;完整
Promise: ×1
chain: ×1

2.2. 源代码 “case2.js”

let promise &＃61; new Promise(function(resolve, reject){console.log(&＃39;Initialize a Promise to Complete Five Things Sequentially 1 -> 2 -> 3 -> 4 -> 5 as follows:&＃39;);resolve();}
);promise.then(function(){var value&＃61;1;console.log("Thing 1, value: ", value);return value;}
).then(function(value){value &＃61; value &＃43; 1;console.log("Thing 2, value: ", value);return value;}
).then(function(value){value &＃61; value &＃43; 1;console.log("Thing 3, value: ", value);return value;}
).then(function(value){value &＃61; value &＃43; 1;console.log("Thing 4, value: ", value);return value;}
).then(function(value){value &＃61; value &＃43; 1;console.log("Thing 5, value: ", value);return value;}
)


2.3. 运行结果

$ node case2.js
Initialize a Promise to Complete Five Things Sequentially 1 -> 2 -> 3 -> 4 -> 5 as follows:
Thing 1, value: 1
Thing 2, value: 2
Thing 3, value: 3
Thing 4, value: 4
Thing 5, value: 5


其他

案例描述

resolve()函数的输入参数&＃xff1a;无
用户函数函数的返回值&＃xff1a;无
函数书写形式&＃xff1a;简化
Promise: ×1
chain: ×1

源代码 “case.js”

let promise &＃61; new Promise((resolve, reject) &＃61;> {console.log(&＃39;Initialize a Promise to Complete Five Things Sequentially 1 -> 2 -> 3 -> 4 -> 5 as follows:&＃39;);resolve();}
);promise.then(() &＃61;> {console.log(&＃39;Thing 1&＃39;);;}
).then(() &＃61;> {console.log(&＃39;Thing 2&＃39;)}
).then(() &＃61;> {console.log(&＃39;Thing 3&＃39;)}
).then(() &＃61;> {console.log(&＃39;Thing 4&＃39;)}
).then(() &＃61;> {console.log(&＃39;Thing 5&＃39;)}
)


运行结果

$ node case.js
Initialize a Promise to Complete Five Things Sequentially 1 -> 2 -> 3 -> 4 -> 5 as follows:
Thing 1
Thing 2
Thing 3
Thing 4
Thing 5