blocks|key|319284|text|请用英文描述一下你想要完成的事情。下面的答案假设您只是想迭代一个名称列表，并对每个名称进行一些处理。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|319285|您希望使用为循环。|offset|length|319286|var+names+=+["beth",+"barry",+"debbie",+"peter"]

for+(var+i=0;+i<names.length;+i%2B%2B)+{
++++//+access+names[i]
}|code-block|syntax|javascript|319287|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for^0|0|5|1|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@$D|U|E|V|1|W]]|A|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

Please give a english description of what you are trying to accomplish. The below answer assumes you simply want to iterate a list of names and do some processing with each.

You want to use a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for" rel="nofollow">for</a> loop.

<pre><code>var names = ["beth", "barry", "debbie", "peter"]

for (var i=0; i&lt;names.length; i++) {
 // access names[i]
}
</code></pre>

blocks|key|2575311|text|您可以使用every测试每个元素是否满足某些条件：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2575312|if+(names.every(function+(name)+{+return+name+}))+{
++//+Do+Something
}|code-block|syntax|javascript|2575313|当找到第一个非真元素时，every将自动停止测试，这可能是一个很大的优化，取决于数组的大小。|2575314|传统上，您只需遍历数组并测试每个元素。您可以使用forEach或简单的for循环来实现这一点。通过从false回调返回forEach，可以在找到非真元素时执行相同的早期终止。|2575315|var+allTrue+=+true;

names.forEach(function+(name)+{
++return+allTrue+=+allTrue+&&+name;
});

if+(allTrue)+{+
++//+Do+something...
}|2575316|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every|1|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach^0|5|5|5|5|0|0|0|C|5|0|O|7|Z|3|1E|5|1N|7|O|7|1|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|H|7|16|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|1A|8|@$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]|$9|1H|A|1I|B|C]]|D|@$9|1J|A|1K|1|1L]]|E|$]]|$1|O|3|P|5|H|7|1M|8|@]|D|@]|E|$I|J]]|$1|Q|3|-4|5|6|7|1N|8|@]|D|@]|E|$]]]|R|$S|$5|T|U|V|E|$W|X]]|Y|$5|T|U|V|E|$W|Z]]]]

You can use <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every" rel="nofollow"><code>every</code></a> to test whether every element satisfies some condition:

<pre><code>if (names.every(function (name) { return name })) {
 // Do Something
}
</code></pre>

<code>every</code> will automatically stop testing when the first non-true element is found, which is potentially a large optimization depending on the size of your array.

Traditionally, you would simply iterate over the array and test each element. You can do so with <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach" rel="nofollow"><code>forEach</code></a> or a simple <code>for</code> loop. You can perform the same early-termination when you find a non-true element by returning <code>false</code> from the <code>forEach</code> callback.

<pre><code>var allTrue = true;

names.forEach(function (name) {
 return allTrue = allTrue &amp;&amp; name;
});

if (allTrue) { 
 // Do something...
}
</code></pre>

blocks|key|967332|text|最好的跨浏览器解决方案是使用传统的for循环。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|967333|var+names+=+["beth",+"barry",+"debbie",+"peter"],
++++isValid+=+true,
++++i;

for+(i+=+0;+i+<+names.length;+i%2B%2B)+{
++++isValid+=+isValid+&&+names[i];
}

if+(isValid)+{
++++//+do+something
}|code-block|syntax|javascript|967334|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|$]]

The best cross-browser solution is to use a traditional for loop. 

<pre><code>var names = ["beth", "barry", "debbie", "peter"],
 isValid = true,
 i;

for (i = 0; i &lt; names.length; i++) {
 isValid = isValid &amp;&amp; names[i];
}

if (isValid) {
 // do something
}
</code></pre>

blocks|key|2575365|text|你可以试试这个；|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2575366|++++var+checkCondition+=+true;
++++for(var+i+=+0;+i<names.length;+i%2B%2B){
++++++if(names[i]+!==+something)+{
+++++++++checkCondition+=+false;
+++++++++break;
++++++}+
++++}
++++if(checkCondition){
++++++++//Do+what+ever+you+like+if+the+condition+holds
++++}else{
++++++++//+Do+whatever+you+like+if+the+condition+does+NOT+holds
++++}|code-block|syntax|javascript|2575367|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|$]]

You can try this;

<pre><code> var checkCondition = true;
 for(var i = 0; i&lt;names.length; i++){
 if(names[i] !== something) {
 checkCondition = false;
 break;
 } 
 }
 if(checkCondition){
 //Do what ever you like if the condition holds
 }else{
 // Do whatever you like if the condition does NOT holds
 }
</code></pre>

blocks|key|321251|text|如果我明白的话，你需要这样的东西|type|unstyled|depth|inlineStyleRanges|entityRanges|data|321252|var+names+=+["beth",+"barry",+"debbie",+"peter"];
var+notUndefinedNames+=+names.filter(function(el){return+el+!==+undefined;});

//+if+all
if+(names.length+===+notUndefinedNames.length)+console.log("You're+all+here.+Great!+Sit+down+and+let's+begin+the+class.");

//+if+one+or+less
else+if+(notUndefinedNames.length+<=+1)+console.log("I+can't+teach+just+one+person.+Class+is+cancelled.");

else+console.log("Welcome+"+%2B+notUndefinedNames.join(',+'));|code-block|syntax|javascript|321253|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|$]]

If i understand right you need something like this

<pre><code>var names = ["beth", "barry", "debbie", "peter"];
var notUndefinedNames = names.filter(function(el){return el !== undefined;});

// if all
if (names.length === notUndefinedNames.length) console.log("You're all here. Great! Sit down and let's begin the class.");

// if one or less
else if (notUndefinedNames.length &lt;= 1) console.log("I can't teach just one person. Class is cancelled.");

else console.log("Welcome " + notUndefinedNames.join(', '));
</code></pre>

I'm very new to JS so go easy on me. I've got this array inside a variable, and am trying to find a better way to write that if statement. So if the names inside that variable grow, I won't need to change the if statement as it won't be hardcoded.

<pre><code>var names = ["beth", "barry", "debbie", "peter"]

if (names[0] &amp;&amp; names [1] &amp;&amp; names [2] &amp;&amp; names [3] {
 Do something...
}
</code></pre>

Something tells me I need to be using the <code>.length</code> property but I can't work out how to properly use it within that statement. Something along the lines of:

<pre><code>if (names[i] * names.length) { 
 Do something...
}
</code></pre>

I know that's wrong. I think need to be finding the index of each and looping through it makign sure it the loop doesn't exceed the amount of values in the array.

Any help is appreciated. Thanks in advance!

Update: Some users have alerted me that my question might not be as clear. I've setup a CodePen here (<a href="http://codepen.io/realph/pen/KjCLd?editors=101" rel="nofollow">http://codepen.io/realph/pen/KjCLd?editors=101</a>) that might explain what I'm trying to achieve.

P.S. How do I stop my from repeating 3 times?

JS: Using Length Property to Write If Statement

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。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

我对JS很陌生，所以别对我太客气了。我把这个数组放在一个变量中，并试图找到一种更好的方法来编写if语句。因此，如果变量中的名称增长，我就不需要更改if语句，因为它不会被硬编码。var names = ["beth", "barry", "debbie", "peter"]if (names[0] && names [1...

问JS:使用Length属性编写If语句
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问JS:使用Length属性编写If语句EN