blocks|key|4426958|text|不要使用reduce。只需使用常规迭代器(for等)对数组进行迭代，并在满足条件时中断。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4426959|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

<p>Don't use reduce. Just iterate on the array with normal iterators (for, etc) and break out when your condition is met.</p>


blocks|key|4426836|text|当然，没有办法让reduce的内置版本过早退出。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4426837|但是您可以编写自己的reduce版本，它使用一个特殊的令牌来确定何时应该中断循环。|4426838|var+EXIT_REDUCE+=+{};

function+reduce(a,+f,+result)+{
++for+(let+i+=+0;+i+<+a.length;+i%2B%2B)+{
++++let+val+=+f(result,+a[i],+i,+a);
++++if+(val+===+EXIT_REDUCE)+break;
++++result+=+val;
++}
++return+result;
}|code-block|syntax|javascript|4426839|像这样使用它，对一个数组求和，但在达到99时退出：|4426840|reduce([1,+2,+99,+3],+(a,+b)+=>+b+===+99+?+EXIT_REDUCE+:+a+%2B+b,+0);

>+3|4426841|entityMap^0|8|6|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|V|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|W|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|X|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|Q|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|R|$]]

<p>There is no way, of course, to get the built-in version of <code>reduce</code> to exit prematurely.</p>

<p>But you can write your own version of reduce which uses a special token to identify when the loop should be broken.</p>

<pre><code>var EXIT_REDUCE = {};

function reduce(a, f, result) {
  for (let i = 0; i &lt; a.length; i++) {
    let val = f(result, a[i], i, a);
    if (val === EXIT_REDUCE) break;
    result = val;
  }
  return result;
}
</code></pre>

<p>Use it like this, to sum an array but exit when you hit 99:</p>

<pre><code>reduce([1, 2, 99, 3], (a, b) =&gt; b === 99 ? EXIT_REDUCE : a + b, 0);

&gt; 3
</code></pre>


blocks|key|4426914|text|Array.every可以提供一种非常自然的机制来中断高阶迭代。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4426915|​|4426916|const+product+=+function(array)+{
++++let+accumulator+=+1;
++++array.every(+factor+=>+{
++++++++accumulator+*=+factor;
++++++++return+!!factor;
++++});
++++return+accumulator;
}
console.log(product([2,2,2,0,2,2]));
//+0|code-block|syntax|javascript|4426917|4426918|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|K|$]]

<p>Array.every can provide a very natural mechanism for breaking out of high order iteration.</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const product = function(array) {
    let accumulator = 1;
    array.every( factor =&gt; {
        accumulator *= factor;
        return !!factor;
    });
    return accumulator;
}
console.log(product([2,2,2,0,2,2]));
// 0</code></pre>
</div>
</div>
</p>


blocks|key|4427052|text|你可以通过抛出一个异常来破坏每一段代码--也就是迭代器中的每一个构建：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4427053|function+breakReduceException(value)+{
++++this.value+=+value
}

try+{
++++Things.reduce(function(memo,+current)+{
++++++++...
++++++++if+(current+<=+0)+throw+new+breakReduceException(memo)
++++++++...
++++},+0)
}+catch+(e)+{
++++if+(e+instanceof+breakReduceException)+var+memo+=+e.value
++++else+throw+e
}|code-block|syntax|javascript|4427054|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

<p>You can break every code - and thus every build in iterator - by throwing an exception:</p>

<pre><code>function breakReduceException(value) {
    this.value = value
}

try {
    Things.reduce(function(memo, current) {
        ...
        if (current &lt;= 0) throw new breakReduceException(memo)
        ...
    }, 0)
} catch (e) {
    if (e instanceof breakReduceException) var memo = e.value
    else throw e
}
</code></pre>


blocks|key|4427381|text|因此，更早地终止使用的习惯用法是arr.splice(0)。这就引出了一个问题，为什么在这种情况下不能只使用arr+=+[]呢？我试过了，reduce忽略了赋值，继续保持不变。reduce习语似乎响应诸如拼接之类的形式，而不响应诸如赋值运算符之类的形式--完全不直观--并且必须作为函数式编程信条中的戒律死记硬背……|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4427382|​|4427383|const+array+=+['9',+'91',+'95',+'96',+'99'];
const+x+=+array
.reduce((acc,+curr,+i,+arr)+=>+{
++++if(i+===+2)+arr.splice(1);++//+eject+early
++++return+acc+%2B=+curr;
++},+'');
console.log('x:+',+x);++//+x:++99195|code-block|syntax|javascript|4427384|4427385|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|K|$]]

<p>So, to terminate even earlier the idiom to use would be arr.splice(0).
Which prompts the question, why can't one just use arr = [] in this case?
I tried it and the reduce ignored the assignment, continuing on unchanged.
The reduce idiom appears to respond to forms such as splice but not forms such as the assignment operator??? - completely unintuitive - and has to be rote-learnt as precepts within the functional programming credo ...</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const array = ['9', '91', '95', '96', '99'];
const x = array
.reduce((acc, curr, i, arr) =&gt; {
    if(i === 2) arr.splice(1);  // eject early
    return acc += curr;
  }, '');
console.log('x: ', x);  // x:  99195</code></pre>
</div>
</div>
</p>


blocks|key|4426859|text|不能从reduce方法内部中断。根据您试图实现的目标，您可以更改最终结果(这可能是您想要这样做的一个原因)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4426860|​|4426861|const+result+=+[1,+1,+1].reduce((a,+b)+=>+a+%2B+b,+0);+//+returns+3

console.log(result);|code-block|syntax|javascript|4426862|4426863|4426864|const+result+=+[1,+1,+1].reduce((a,+b,+c,+d)+=>+{
++if+(c+===+1+&&+b+<+3)+{
++++return+a+%2B+b+%2B+1;
++}+
++return+a+%2B+b;
},+0);+//+now+returns+4

console.log(result);|4426865|4426866|请记住:您不能直接重新分配数组参数|4426867|4426868|const+result+=+[1,+1,+1].reduce(+(a,+b,+c,+d)+=>+{
++if+(c+===+0)+{
++++d+=+[1,+1,+2];
++}+
++return+a+%2B+b;
},+0);+//+still+returns+3

console.log(result);|4426869|4426870|但是(如下所述)，您可以通过更改数组的内容来影响结果：|4426871|4426872|const+result+=+[1,+1,+1].reduce(+(a,+b,+c,+d)+=>+{
++if+(c+===+0)+{
++++d[2]+=+100;
++}+
++return+a+%2B+b;
},+0);+//+now+returns+102

console.log(result);|4426873|4426874|entityMap^0|3|6|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|15|8|@$9|16|A|17|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|18|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|19|8|@]|D|@]|E|$K|L]]|$1|M|3|G|5|6|7|1A|8|@]|D|@]|E|$]]|$1|N|3|G|5|6|7|1B|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1C|8|@]|D|@]|E|$K|L]]|$1|Q|3|G|5|6|7|1D|8|@]|D|@]|E|$]]|$1|R|3|S|5|6|7|1E|8|@]|D|@]|E|$]]|$1|T|3|G|5|6|7|1F|8|@]|D|@]|E|$]]|$1|U|3|V|5|J|7|1G|8|@]|D|@]|E|$K|L]]|$1|W|3|G|5|6|7|1H|8|@]|D|@]|E|$]]|$1|X|3|Y|5|6|7|1I|8|@]|D|@]|E|$]]|$1|Z|3|G|5|6|7|1J|8|@]|D|@]|E|$]]|$1|10|3|11|5|J|7|1K|8|@]|D|@]|E|$K|L]]|$1|12|3|G|5|6|7|1L|8|@]|D|@]|E|$]]|$1|13|3|-4|5|6|7|1M|8|@]|D|@]|E|$]]]|14|$]]

<p>You cannot break from inside of a <code>reduce</code> method. Depending on what you are trying to accomplish you could alter the final result (which is one reason you may want to do this)</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const result = [1, 1, 1].reduce((a, b) =&gt; a + b, 0); // returns 3

console.log(result);</code></pre>
</div>
</div>
</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const result = [1, 1, 1].reduce((a, b, c, d) =&gt; {
  if (c === 1 &amp;&amp; b &lt; 3) {
    return a + b + 1;
  } 
  return a + b;
}, 0); // now returns 4

console.log(result);</code></pre>
</div>
</div>
</p>
<p>Keep in mind: you cannot reassign the array parameter directly</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const result = [1, 1, 1].reduce( (a, b, c, d) =&gt; {
  if (c === 0) {
    d = [1, 1, 2];
  } 
  return a + b;
}, 0); // still returns 3

console.log(result);</code></pre>
</div>
</div>
</p>
<p>However (as pointed out below), you CAN affect the outcome by changing the array's contents:</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const result = [1, 1, 1].reduce( (a, b, c, d) =&gt; {
  if (c === 0) {
    d[2] = 100;
  } 
  return a + b;
}, 0); // now returns 102

console.log(result);</code></pre>
</div>
</div>
</p>


blocks|key|4427093|text|由于promise具有resolve和reject回调参数，因此我使用break回调参数创建了reduce变通方法函数。它接受所有与原生reduce方法相同的参数，除了第一个参数是一个要处理的数组(避免猴子修补)。第三个2+initialValue参数是可选的。有关function+reducer，请参阅下面的代码片段。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4427094|​|4427095|var+list+=+["w","o","r","l","d","+","p","i","e","r","o","g","i"];

var+result+=+reducer(list,(total,current,index,arr,stop)=>{
++if(current+===+"+")+stop();+//when+called,+the+loop+breaks
++return+total+%2B+current;
},'hello+');

console.log(result);+//hello+world

function+reducer(arr,+callback,+initial)+{
++var+hasInitial+=+arguments.length+>=+3;
++var+total+=+hasInitial+?+initial+:+arr[0];
++var+breakNow+=+false;
++for+(var+i+=+hasInitial+?+0+:+1;+i+<+arr.length;+i%2B%2B)+{
++++var+currentValue+=+arr[i];
++++var+currentIndex+=+i;
++++var+newTotal+=+callback(total,+currentValue,+currentIndex,+arr,+()+=>+breakNow+=+true);
++++if+(breakNow)+break;
++++total+=+newTotal;
++}
++return+total;
}|code-block|syntax|javascript|4427096|4427097|下面是作为阵列method修改后的脚本的reducer：|4427098|Array.prototype.reducer+=+function(callback,initial){
++var+hasInitial+=+arguments.length+>=+2;
++var+total+=+hasInitial+?+initial+:+this[0];
++var+breakNow+=+false;
++for+(var+i+=+hasInitial+?+0+:+1;+i+<+this.length;+i%2B%2B)+{
++++var+currentValue+=+this[i];
++++var+currentIndex+=+i;
++++var+newTotal+=+callback(total,+currentValue,+currentIndex,+this,+()+=>+breakNow+=+true);
++++if+(breakNow)+break;
++++total+=+newTotal;
++}
++return+total;
};

var+list+=+["w","o","r","l","d","+","p","i","e","r","o","g","i"];

var+result+=+list.reducer((total,current,index,arr,stop)=>{
++if(current+===+"+")+stop();+//when+called,+the+loop+breaks
++return+total+%2B+current;
},'hello+');


console.log(result);|4427099|entityMap^0|2|7|B|7|J|6|Z|5|1B|6|1W|6|34|C|3P|8|0|0|0|0|7|6|K|7|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]|$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1A|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1B|8|@]|D|@]|E|$K|L]]|$1|M|3|G|5|6|7|1C|8|@]|D|@]|E|$]]|$1|N|3|O|5|6|7|1D|8|@$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]]|D|@]|E|$]]|$1|P|3|Q|5|J|7|1I|8|@]|D|@]|E|$K|L]]|$1|R|3|-4|5|6|7|1J|8|@]|D|@]|E|$]]]|S|$]]

<p>As the <code>promise</code>s have <code>resolve</code> and <code>reject</code> callback arguments, I created the <code>reduce</code> workaround function with the <code>break</code> callback argument. It takes all the same arguments as native <code>reduce</code> method, except the first one is an array to work on (avoid monkey patching). The third [2] <code>initialValue</code> argument is optional. See the snippet below for the <code>function</code> reducer.</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>var list = ["w","o","r","l","d"," ","p","i","e","r","o","g","i"];

var result = reducer(list,(total,current,index,arr,stop)=&gt;{
  if(current === " ") stop(); //when called, the loop breaks
  return total + current;
},'hello ');

console.log(result); //hello world

function reducer(arr, callback, initial) {
  var hasInitial = arguments.length &gt;= 3;
  var total = hasInitial ? initial : arr[0];
  var breakNow = false;
  for (var i = hasInitial ? 0 : 1; i &lt; arr.length; i++) {
    var currentValue = arr[i];
    var currentIndex = i;
    var newTotal = callback(total, currentValue, currentIndex, arr, () =&gt; breakNow = true);
    if (breakNow) break;
    total = newTotal;
  }
  return total;
}</code></pre>
</div>
</div>
</p>

<p>And here is the <code>reducer</code> as an Array <code>method</code> modified script:</p>

<pre><code>Array.prototype.reducer = function(callback,initial){
  var hasInitial = arguments.length &gt;= 2;
  var total = hasInitial ? initial : this[0];
  var breakNow = false;
  for (var i = hasInitial ? 0 : 1; i &lt; this.length; i++) {
    var currentValue = this[i];
    var currentIndex = i;
    var newTotal = callback(total, currentValue, currentIndex, this, () =&gt; breakNow = true);
    if (breakNow) break;
    total = newTotal;
  }
  return total;
};

var list = ["w","o","r","l","d"," ","p","i","e","r","o","g","i"];

var result = list.reducer((total,current,index,arr,stop)=&gt;{
  if(current === " ") stop(); //when called, the loop breaks
  return total + current;
},'hello ');


console.log(result);
</code></pre>


blocks|key|4427193|text|Reduce+functional+version+with+break可以实现为'transform'，例如。在下划线中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4427194|我尝试用一个config标志来停止它的实现，这样实现reduce就不必改变您当前使用的数据结构。|4427195|const+transform+=+(arr,+reduce,+init,+config+=+{})+=>+{
++const+result+=+arr.reduce((acc,+item,+i,+arr)+=>+{
++++if+(acc.found)+return+acc

++++acc.value+=+reduce(config,+acc.value,+item,+i,+arr)

++++if+(config.stop)+{
++++++acc.found+=+true
++++}

++++return+acc
++},+{+value:+init,+found:+false+})

++return+result.value
}

module.exports+=+transform|code-block|syntax|javascript|4427196|Usage1，简单的一个|4427197|const+a+=+[0,+1,+1,+3,+1]

console.log(transform(a,+(config,+acc,+v)+=>+{
++if+(v+===+3)+{+config.stop+=+true+}
++if+(v+===+1)+return+%2B%2Bacc
++return+acc
},+0))|4427198|配置，使用Usage2作为内部变量|4427199|const+pixes+=+Array(size).fill(0)
const+pixProcessed+=+pixes.map((_,+pixId)+=>+{
++return+transform(pics,+(config,+_,+pic)+=>+{
++++if+(pic[pixId]+!==+'2')+config.stop+=+true+
++++return+pic[pixId]
++},+'0')
})|4427200|Usage3，将配置捕获为外部变量|4427201|const+thrusts2+=+permute([9,+8,+7,+6,+5]).map(signals+=>+{
++const+datas+=+new+Array(5).fill(_data())
++const+ps+=+new+Array(5).fill(0)

++let+thrust+=+0,+config
++do+{

++++config+=+{}
++++thrust+=+transform(signals,+(_config,+acc,+signal,+i)+=>+{
++++++const+res+=+intcode(
++++++++datas[i],+signal,
++++++++{+once:+true,+i:+ps[i],+prev:+acc+}
++++++)

++++++if+(res)+{
++++++++[ps[i],+acc]+=+res+
++++++}+else+{
++++++++_config.stop+=+true
++++++}

++++++return+acc
++++},+thrust,+config)

++}+while+(!config.stop)

++return+thrust
},+0)|4427202|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|11|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|13|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

<p>Reduce functional version with break can be implemented as 'transform', ex. in underscore.</p>

<p>I tried to implement it with a config flag to stop it so that the implementation reduce doesn't have to change the data structure that you are currently using.  </p>

<pre><code>const transform = (arr, reduce, init, config = {}) =&gt; {
  const result = arr.reduce((acc, item, i, arr) =&gt; {
    if (acc.found) return acc

    acc.value = reduce(config, acc.value, item, i, arr)

    if (config.stop) {
      acc.found = true
    }

    return acc
  }, { value: init, found: false })

  return result.value
}

module.exports = transform
</code></pre>

<p>Usage1, simple one</p>

<pre><code>const a = [0, 1, 1, 3, 1]

console.log(transform(a, (config, acc, v) =&gt; {
  if (v === 3) { config.stop = true }
  if (v === 1) return ++acc
  return acc
}, 0))
</code></pre>

<p>Usage2, use config as internal variable</p>

<pre><code>const pixes = Array(size).fill(0)
const pixProcessed = pixes.map((_, pixId) =&gt; {
  return transform(pics, (config, _, pic) =&gt; {
    if (pic[pixId] !== '2') config.stop = true 
    return pic[pixId]
  }, '0')
})
</code></pre>

<p>Usage3, capture config as external variable</p>

<pre><code>const thrusts2 = permute([9, 8, 7, 6, 5]).map(signals =&gt; {
  const datas = new Array(5).fill(_data())
  const ps = new Array(5).fill(0)

  let thrust = 0, config
  do {

    config = {}
    thrust = transform(signals, (_config, acc, signal, i) =&gt; {
      const res = intcode(
        datas[i], signal,
        { once: true, i: ps[i], prev: acc }
      )

      if (res) {
        [ps[i], acc] = res 
      } else {
        _config.stop = true
      }

      return acc
    }, thrust, config)

  } while (!config.stop)

  return thrust
}, 0)
</code></pre>


blocks|key|4427021|text|我用来解决同样问题的另一个简单的实现：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4427022|function+reduce(array,+reducer,+first)+{
++let+result+=+first+%7C%7C+array.shift()

++while+(array.length+>+0)+{
++++result+=+reducer(result,+array.shift())
++++if+(result+&&+result.reduced)+{
++++++return+result.reduced
++++}
++}

++return+result
}|code-block|syntax|javascript|4427023|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

<p>Another simple implementation that I came with solving the same issue:</p>

<pre><code>function reduce(array, reducer, first) {
  let result = first || array.shift()

  while (array.length &gt; 0) {
    result = reducer(result, array.shift())
    if (result &amp;&amp; result.reduced) {
      return result.reduced
    }
  }

  return result
}
</code></pre>


blocks|key|4427120|text|如果您想使用下面的模式按顺序使用reduce链接promises：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4427121|return+[1,2,3,4].reduce(function(promise,n,i,arr){
+++return+promise.then(function(){
+++++++//+this+code+is+executed+when+the+reduce+loop+is+terminated,
+++++++//+so+truncating+arr+here+or+in+the+call+below+does+not+works
+++++++return+somethingReturningAPromise(n);
+++});
},+Promise.resolve());|code-block|syntax|javascript|4427122|但是需要根据promise内部或外部发生的事情来中断事情变得有点复杂，因为reduce循环在第一个promise被执行之前被终止，使得在promise回调中截断数组变得无用，我以这个实现结束：|4427123|function+reduce(array,+promise,+fn,+i)+{
++i=i%7C%7C0;
++return+promise
++.then(function(){
++++return+fn(promise,array[i]);
++})
++.then(function(result){
++++if+(!promise.break+&&+%2B%2Bi<array.length)+{
++++++return+reduce(array,promise,fn,i);
++++}+else+{
++++++return+result;
++++}
++})
}|4427124|然后你可以这样做：|4427125|var+promise=Promise.resolve();
reduce([1,2,3,4],promise,function(promise,val){
++return+iter(promise,+val);
}).catch(console.error);

function+iter(promise,+val)+{
++return+new+Promise(function(resolve,+reject){
++++setTimeout(function(){
++++++if+(promise.break)+return+reject('break');
++++++console.log(val);
++++++if+(val==3)+{promise.break=true;}
++++++resolve(val);
++++},+4000-1000*val);
++});
}|4427126|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

<p>If you want to chain promises sequentially with reduce using the pattern below:</p>

<pre><code>return [1,2,3,4].reduce(function(promise,n,i,arr){
   return promise.then(function(){
       // this code is executed when the reduce loop is terminated,
       // so truncating arr here or in the call below does not works
       return somethingReturningAPromise(n);
   });
}, Promise.resolve());
</code></pre>

<p>But need to break according to something happening inside or outside a promise
things become a little bit more complicated because the reduce loop is terminated before the first promise is executed, making truncating the array in the promise callbacks useless, I ended up with this implementation:</p>

<pre><code>function reduce(array, promise, fn, i) {
  i=i||0;
  return promise
  .then(function(){
    return fn(promise,array[i]);
  })
  .then(function(result){
    if (!promise.break &amp;&amp; ++i&lt;array.length) {
      return reduce(array,promise,fn,i);
    } else {
      return result;
    }
  })
}
</code></pre>

<p>Then you can do something like this:</p>

<pre><code>var promise=Promise.resolve();
reduce([1,2,3,4],promise,function(promise,val){
  return iter(promise, val);
}).catch(console.error);

function iter(promise, val) {
  return new Promise(function(resolve, reject){
    setTimeout(function(){
      if (promise.break) return reject('break');
      console.log(val);
      if (val==3) {promise.break=true;}
      resolve(val);
    }, 4000-1000*val);
  });
}
</code></pre>


blocks|key|4427253|text|我像下面这样解决了这个问题，例如，在some方法中，短路可以节省很多成本：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4427254|​|4427255|const+someShort+=+(list,+fn)+=>+{
++let+t;
++try+{
++++return+list.reduce((acc,+el)+=>+{
++++++t+=+fn(el);
++++++console.log('found+?',+el,+t)
++++++if+(t)+{
++++++++throw+''
++++++}
++++++return+t
++++},+false)
++}+catch+(e)+{
++++return+t
++}
}

const+someEven+=+someShort([1,+2,+3,+1,+5],+el+=>+el+%25+2+===+0)

console.log(someEven)|code-block|syntax|javascript|4427256|4427257|entityMap^0|I|4|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|S|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|T|8|@]|D|@]|E|$K|L]]|$1|M|3|G|5|6|7|U|8|@]|D|@]|E|$]]|$1|N|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|O|$]]

<p>I solved it like follows, for example in the <code>some</code> method where short circuiting can save a lot:</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const someShort = (list, fn) =&gt; {
  let t;
  try {
    return list.reduce((acc, el) =&gt; {
      t = fn(el);
      console.log('found ?', el, t)
      if (t) {
        throw ''
      }
      return t
    }, false)
  } catch (e) {
    return t
  }
}

const someEven = someShort([1, 2, 3, 1, 5], el =&gt; el % 2 === 0)

console.log(someEven)</code></pre>
</div>
</div>
</p>


<p>How can I break the iteration of <code>reduce()</code> method?</p>
<p><code>for</code>:</p>
<pre><code>for (var i = Things.length - 1; i &gt;= 0; i--) {
  if(Things[i] &lt;= 0){
    break;
  }
};
</code></pre>
<p><code>reduce()</code></p>
<pre><code>Things.reduce(function(memo, current){
  if(current &lt;= 0){
    //break ???
    //return; &lt;-- this will return undefined to memo, which is not what I want
  }
}, 0)
</code></pre>


How to early break reduce() method?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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如何打破reduce()方法的迭代？forfor (var i = Things.length - 1; i >= 0; i--) {  if(Things[i] <= 0){    break;  }};reduce()Things.reduce(function(memo, current){  if(current <= 0){    //break ???    //return; <--

问如何提前中断reduce()方法？
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