node.js if-else 流在承诺中（蓝鸟）
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if-else flow in promise (bluebird)
提问by vinayr
This is a short version of my code.
这是我的代码的简短版本。
var Promise = require('bluebird');
var fs = Promise.promisifyAll(require("fs"));
if (conditionA) {
fs.writeFileAsync(file, jsonData).then(function() {
return functionA();
});
} else {
functionA();
}
Both conditions call functionA. Is there way to avoid else condition? I can do fs.writeFileSyncbut I am looking for a non-blocking solution.
两个条件都调用functionA。有没有办法避免其他条件？我可以，fs.writeFileSync但我正在寻找非阻塞解决方案。
回答by Bergi
I think you're looking for
我想你正在寻找
(conditionA
? fs.writeFileAsync(file, jsonData)
: Promise.resolve())
.then(functionA);
which is short for
这是缩写
var waitFor;
if (conditionA)
waitFor = fs.writeFileAsync(file, jsonData);
else
waitFor = Promise.resolve(undefined); // wait for nothing,
// create fulfilled promise
waitFor.then(function() {
return functionA();
});
回答by Goblinlord
While other suggestions here work, personally I prefer the following.
虽然这里的其他建议有效，但我个人更喜欢以下建议。
Promise.resolve(function(){
if (condition) return fs.writeFileAsync(file, jsonData);
}())
.then()
It has the disadvantage of always creating this additional promise (rather minor IMO) but looks much cleaner to my eye. You can also add other conditions/logic easily inside the IIFE.
它的缺点是总是创建这个额外的承诺（相当小的 IMO），但在我看来看起来更干净。您还可以在 IIFE 中轻松添加其他条件/逻辑。
EDIT
编辑
After implementing things like this for a long time now I have definitely changed to something slightly clearer. The initial promise is created regardless so it is much clearer to simply do:
在实施这样的事情很长一段时间之后，我肯定已经改变了一些更清晰的东西。无论如何都会创建初始承诺，因此简单地执行以下操作会更清晰：
/* Example setup */
var someCondition = (Math.random()*2)|0;
var value = "Not from a promise";
var somePromise = new Promise((resolve) => setTimeout(() => resolve('Promise value'), 3000));
/* Example */
Promise.resolve()
.then(() => {
if (someCondition) return value;
return somePromise;
})
.then((result) => document.body.innerHTML = result);Initial stateif (someCondition) return somePromise;
inside of the first .then() function.
在第一个 .then() 函数内部。
回答by aarosil
You could always use Promise.all()with conditional function
你总是可以使用Promise.all()条件函数
var condition = ...;
var maybeWrite = function(condition, file, jsonData){
return (condition) ? fs.writeFileAsync(file, jsonData) : Promise.resolve(true);
}
Promise.all([maybeWrite(condition, file, jsonData),functionA()])
.then(function(){
// here 'functionA' was called, 'writeFileAsync' was maybe called
})
Or, if you want functionAonly called after the file maybe was written you can separate:
或者，如果您只想functionA在文件写入后调用，您可以分开：
maybeWrite(condition, file, jsonData)
.then(function(){
// here file may have been written, you can call 'functionA'
return functionA();
})
