Why does delete operator return true if I try to delete non existing indexed element of an array?

More precisely deletion of undefined is true in javascript?

var arr = ['a','b','c','d'];

console.log(delete arr[2000]);  //true why?

console.log(delete aaaaa);     //true  why not reference error?

console.log(delete arrr[2000]);  //reference error  it's okay i think

I don't understand difference between 2nd and 3rd deletion. Both should ideally give reference error.

Why does delete operator return true if I try to delete non existing indexed element of an array?

More precisely deletion of undefined is true in javascript?

var arr = ['a','b','c','d'];

console.log(delete arr[2000]);  //true why?

console.log(delete aaaaa);     //true  why not reference error?

console.log(delete arrr[2000]);  //reference error  it's okay i think

I don't understand difference between 2nd and 3rd deletion. Both should ideally give reference error.

• javascript
• arrays

Share Improve this question Follow edited Aug 18, 2015 at 19:54 Brian Tompsett - 汤莱恩 5,8937272 gold badges6161 silver badges133133 bronze badges asked Jan 5, 2012 at 20:25 P KP K 10.2k1313 gold badges5656 silver badges9999 bronze badges 4

• 1 because it worked, arr[2000] is not there anymore. – zzzzBov Commented Jan 5, 2012 at 20:26
• do u mean deletion of undefined is true? arr[2000] was undefined – P K Commented Jan 5, 2012 at 20:27
• The real question is what are you trying to do, this might be a classical XY Problem case. – Madara's Ghost Commented Jan 5, 2012 at 20:30
• updated my answer to your edits – Andreas Köberle Commented Jan 5, 2012 at 20:45

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1 Answer 1

Sorted by: Reset to default 9

From the MDN:

Returns false only if the property exists and cannot be deleted. It returns true in all other cases.

edit:

here you just delete a in your scope, mostly the window scope

console.log(delete aaaaa);     //true  why not reference error?

so its the same as:

console.log(delete window.aaaaa);     //true  

here arrr is undefined and you get an reference error before the delete method is called

console.log(delete arrr[2000]);  //reference error  it's okay i think