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Javascript puzzle

SgtBot
By SgtBot
in Programming
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Posted

I've been practicing a lot of html and javascript recently, and I came across this challenge question. I can't for the life of me figure out why it works and I feel like the answer is very simple.

Here it is:

What is the output of this code: 

<html>
<head>
<title>Test</title>
</head>
<body>
 <script type="text/javascript">
  var arr = [1,2,3,4];
  arr[arr[1]]=5;
  alert(arr);
 </script>
</body>
</html>

The answer is 1,2,5,4 but I can't figure out why. arr[1] is the second spot in the array, so the output should be 1,5,3,4 but its not. Does anybody know how this works? It's been bugging me for hours. Thanks!

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Posted

It's because programming arrays start with 0, so arr[1] is the second value in the array.

"We're all in this together, might as well be friends" Tom, Toonami.

 

mini eLiXiVy: my open source 65% mechanical PCB, a build log, PCB anatomy and discussing open source licenses: https://linustechtips.com/topic/1366493-elixivy-a-65-mechanical-keyboard-build-log-pcb-anatomy-and-how-i-open-sourced-this-project/

 

mini_cardboard: a 4% keyboard build log and how keyboards work: https://linustechtips.com/topic/1328547-mini_cardboard-a-4-keyboard-build-log-and-how-keyboards-work/

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1 minute ago, Minibois said:

It's because programming arrays start with 0, so arr[1] is the second value in the array.

It's not changing the second number, its changing the third number. It should change the second but it doesn't I ran it myself its changing the 3 to a 5.

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Posted

so arr[1] gives back 2 -->  this value is inserted into the second arr[] so it selects the 3 position of the original array which is the 3 and you override it with 5

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Just now, SgtBot said:

It's not changing the second number, its changing the third number. It should change the second but it doesn't I ran it myself its changing the 3 to a 5.

Yea, just re-read your post and noticed I missed a dot, which caused me to misinterpret what you said. Sorry about that!

But I see someone else correctly answered your question here.

"We're all in this together, might as well be friends" Tom, Toonami.

 

mini eLiXiVy: my open source 65% mechanical PCB, a build log, PCB anatomy and discussing open source licenses: https://linustechtips.com/topic/1366493-elixivy-a-65-mechanical-keyboard-build-log-pcb-anatomy-and-how-i-open-sourced-this-project/

 

mini_cardboard: a 4% keyboard build log and how keyboards work: https://linustechtips.com/topic/1328547-mini_cardboard-a-4-keyboard-build-log-and-how-keyboards-work/

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1 minute ago, Helibert said:

so arr[1] gives back 2 -->  this value is inserted into the second arr[] so it selects the 3 position of the original array which is the 3 and you override it with 5

Oh my god I fking knew it was simple idk why I couldn't see that.

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