async.waterfall 在 Node.js 的 For 循环中
async.waterfall in a For Loop in Node.js
在 for
循环中使用 async.waterfall
时,似乎 for
循环在嵌套的 async.waterfall
完成其所有步骤之前进行迭代。如何避免这种情况?
for(var i = 0; i < users.length; i++ ) {
console.log(i)
async.waterfall([
function(callback) {
callback(null, 'one', 'two');
},
function(arg1, arg2, callback) {
// arg1 now equals 'one' and arg2 now equals 'two'
callback(null, 'three');
},
function(arg1, callback) {
// arg1 now equals 'three'
callback(null, 'done');
}
], function (err, result) {
// result now equals 'done'
console.log('done')
});
}
输出
0
1
2
3
4
done
done
done
done
done
期望输出
0
done
1
done
2
done
3
done
4
done
您需要应用递归模式。我的建议是这样的
function foo(properties, callback){
/*Initialize inputs w/ useful defaults. Using a properties object simply because it looks nicer, you can use individual values if you'd like.*/
properties.start = properties.start || 0;
properties.end = properties.end || 10; //or any default length
properties.data = properties.data || [];
async.waterfall([
function(callback) {
},
function(arg1, arg2, callback) {
/* arg1 now equals 'one' and arg2 now equals 'two' you can do something with that before continuing processing */
},
function(arg1, callback) {
/* arg1 now equals 'three', you can do something with that before continuing processing */
}
], function (err, result) {
// result now equals 'done'
// now that we have fully processed one record, we need to either finish or recurse to the next element.
if(properties.index >= properties.end){
callback();
}
else{
properties.index++;
foo(properties, callback);
}
})}
我已将回调传递给每个函数回调。如果你愿意,你可以选择以这种方式提前结束递归,或者你可以在那个地方做你想做的任何其他事情。这类似于我最近提出的一个问题: 也有一些其他有趣的问题解决方案。
你可以像这样使用 async 的 forEachLimit
var async = require("async")
var users = []; // Initialize user array or get it from DB
async.forEachLimit(users, 1, function(user, userCallback){
async.waterfall([
function(callback) {
callback(null, 'one', 'two');
},
function(arg1, arg2, callback) {
// arg1 now equals 'one' and arg2 now equals 'two'
callback(null, 'three');
},
function(arg1, callback) {
// arg1 now equals 'three'
callback(null, 'done');
}
], function (err, result) {
// result now equals 'done'
console.log('done')
userCallback();
});
}, function(err){
console.log("User For Loop Completed");
});
在 for
循环中使用 async.waterfall
时,似乎 for
循环在嵌套的 async.waterfall
完成其所有步骤之前进行迭代。如何避免这种情况?
for(var i = 0; i < users.length; i++ ) {
console.log(i)
async.waterfall([
function(callback) {
callback(null, 'one', 'two');
},
function(arg1, arg2, callback) {
// arg1 now equals 'one' and arg2 now equals 'two'
callback(null, 'three');
},
function(arg1, callback) {
// arg1 now equals 'three'
callback(null, 'done');
}
], function (err, result) {
// result now equals 'done'
console.log('done')
});
}
输出
0
1
2
3
4
done
done
done
done
done
期望输出
0
done
1
done
2
done
3
done
4
done
您需要应用递归模式。我的建议是这样的
function foo(properties, callback){
/*Initialize inputs w/ useful defaults. Using a properties object simply because it looks nicer, you can use individual values if you'd like.*/
properties.start = properties.start || 0;
properties.end = properties.end || 10; //or any default length
properties.data = properties.data || [];
async.waterfall([
function(callback) {
},
function(arg1, arg2, callback) {
/* arg1 now equals 'one' and arg2 now equals 'two' you can do something with that before continuing processing */
},
function(arg1, callback) {
/* arg1 now equals 'three', you can do something with that before continuing processing */
}
], function (err, result) {
// result now equals 'done'
// now that we have fully processed one record, we need to either finish or recurse to the next element.
if(properties.index >= properties.end){
callback();
}
else{
properties.index++;
foo(properties, callback);
}
})}
我已将回调传递给每个函数回调。如果你愿意,你可以选择以这种方式提前结束递归,或者你可以在那个地方做你想做的任何其他事情。这类似于我最近提出的一个问题:
你可以像这样使用 async 的 forEachLimit
var async = require("async")
var users = []; // Initialize user array or get it from DB
async.forEachLimit(users, 1, function(user, userCallback){
async.waterfall([
function(callback) {
callback(null, 'one', 'two');
},
function(arg1, arg2, callback) {
// arg1 now equals 'one' and arg2 now equals 'two'
callback(null, 'three');
},
function(arg1, callback) {
// arg1 now equals 'three'
callback(null, 'done');
}
], function (err, result) {
// result now equals 'done'
console.log('done')
userCallback();
});
}, function(err){
console.log("User For Loop Completed");
});