How do I empty an array in JavaScript

Question

Is there a way to empty an array and if so possibly with  remove     For instance    A    1 2 3 4     How can I empty that

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Performance test   http   jsperf com array-clear-methods 3  a          37  slower a length   0     89  slower a splice 0  a length      97  slower while  a length  gt  0        a pop         Fastest

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If you need to keep the original array because you have other references to it that should be updated too  you can clear it without creating a new array by setting its length to zero   A length   0

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If you are using   a          Then you are assigning new array reference to a  if reference in a is already assigned to any other variable  then it will not empty that array too and hence garbage collector will not collect that memory   For ex    var a  1 2 3   var b a  a     console log b     It will print  1 2 3     or  a length   0    When we specify a length  we are just resetting boundaries of the array and memory for rest array elements will be connected by garbage collector    Instead of these two solutions are better   a splice 0 a length    and  while a length  gt  0        a pop        As per previous answer by kenshou html  second method is faster

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In case you are interested in the memory allocation  you may compare each approach using something like this jsfiddle in conjunction with chrome dev tools  timeline tab  You will want to use the trash bin icon at the bottom to force a garbage collection after  clearing  the array  This should give you a more definite answer for the browser of your choice  A lot of answers here are old and I wouldn t rely on them but rather test as in  tanguy k s answer above    for an intro to the aforementioned tab you can check out here   Stackoverflow forces me to copy the jsfiddle so here it is    lt html gt   lt script gt  var size   1000 100 window onload   function       document getElementById  quantifier   value   size    function scaffold       console log  processing Scaffold         a   new Array   function start       size   document getElementById  quantifier   value   console log  Starting    quantifier is     size     console log  starting test     for  i 0  i lt size  i         a i   something        console log  done         function tearDown       console log  processing teardown      a length 0     lt  script gt   lt body gt       lt span style  color green   gt Quantifier  lt  span gt       lt input id  quantifier  style  color green   type  text  gt  lt  input gt       lt button onclick  scaffold    gt Scaffold lt  button gt       lt button onclick  start    gt Start lt  button gt       lt button onclick  tearDown    gt Clean lt  button gt       lt br  gt   lt  body gt   lt  html gt    And you should take note that it may depend on the type of the array elements  as javascript manages strings differently than other primitive types  not to mention arrays of objects  The type may affect what happens

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To Empty a Current memory location of an array use   myArray length   0  or  myArray pop   UN-till its length is 0    length   You can set the length property to truncate an array at any time  When you extend an array by changing its length property  the number of actual elements increases  pop      The pop method removes the last element from an array and returns that returns the removed value  shift     The shift method removes the element at the zeroeth index and shifts the values at consecutive indexes down  then returns the removed value    Example   var arr     77    arr length   20  console log  Increasing      arr       20    77   empty    19  arr length   12  console log  Truncating      arr       12    77   empty    11   var mainArr   new Array    mainArr     1    2    3    4     var refArr   mainArr  console log  Current   mainArr   Refered   refArr    refArr length   3  console log  Length    Current   mainArr   Refered   refArr    mainArr push  0    console log  Push to the End of Current Array Memory Location  n  Current   mainArr   Refered   refArr    mainArr poptill length 0   console log  Empty Array  n  Current   mainArr   Refered   refArr    Array prototype poptill length   function  e      while  this length        if  this length    e   break       console log  removed last element    this pop                 new Array        Create an Array with new memory location by using Array constructor or array literal   mainArr          a new empty array is addressed to mainArr   var arr   new Array  10       Array constructor arr unshift  1       add to the front arr push  15       add to the end console log  After Adding      arr        1    10    15    arr pop       remove from the end arr shift       remove from the front console log  After Removing      arr        10    var arrLit     14    17    console log  array literal       indexedItem  arrLit          0 14  1 17   function indexedItem  arr         var indexedStr           arr forEach function item  index  array            indexedStr        index     item              console log item  index               return indexedStr     slice     By using slice function we get an shallow copy of elements from the original array  with new memory address  So that any modification on cloneArr will not affect to an actual original array   var shallowCopy   mainArr slice       this is how to make a copy  var cloneArr   mainArr slice 0  3    console log  Main   mainArr    tCloned   cloneArr    cloneArr length   0     Clears current memory location of an array  console log  Main   mainArr    tCloned   cloneArr

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You can easily create a function to do that for you  change the length or even add it to native Array as remove   function for reuse   Imagine you have this array   var arr    1  2  3  4  5     the array   OK  just simply run this   arr length   0    change the length   and the result is        result   easy way to empty an array     Also using loop which is not necessary but just another way to do that      could be arr pop   or arr splice 0  don t need to return as main array get changed     function remove arr      while arr length        arr shift             There are also tricky way which you can think about  for example something like this   arr splice 0  arr length          So if arr has 5 items  it will splice 5 items from 0  which means nothing will remain in the array   Also other ways like simply reassign the array for example   arr              If you look at the Array functions  there are many other ways to do this  but the most recommended one could be changing the length   As I said in the first place  you can also prototype remove   as it s the answer to your question  you can simply choose one of the methods above and prototype it to Array object in JavaScript  something like   Array prototype remove   Array prototype remove    function       this splice 0  this length        and you can simply call it like this to empty any array in your javascript application   arr remove

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Use below if you need to empty Angular 2  FormArray    public emptyFormArray formArray FormArray        for  let i   formArray controls length - 1  i  gt   0  i--            formArray removeAt i

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Ways to clear an existing array A   Method 1   this was my original answer to the question   A         This code will set the variable A to a new empty array  This is perfect if you don t have references to the original array A anywhere else because this actually creates a brand new  empty  array  You should be careful with this method because if you have referenced this array from another variable or property  the original array will remain unchanged  Only use this if you only reference the array by its original variable A   This is also the fastest solution   This code sample shows the issue you can encounter when using this method   var arr1     a   b   c   d   e   f    var arr2   arr1      Reference arr1 by another variable  arr1       console log arr2      Output   a   b   c   d   e   f     Method 2  as suggested by Matthew Crumley   A length   0   This will clear the existing array by setting its length to 0  Some have argued that this may not work in all implementations of JavaScript  but it turns out that this is not the case  It also works when using  strict mode  in ECMAScript 5 because the length property of an array is a read write property   Method 3  as suggested by Anthony   A splice 0 A length    Using  splice   will work perfectly  but since the  splice   function will return an array with all the removed items  it will actually return a copy of the original array  Benchmarks suggest that this has no effect on performance whatsoever   Method 4  as suggested by tanguy k   while A length  gt  0        A pop        This solution is not very succinct  and it is also the slowest solution  contrary to earlier benchmarks referenced in the original answer   Performance  Of all the methods of clearing an existing array  methods 2 and 3 are very similar in performance and are a lot faster than method 4  See this benchmark   As pointed out by Diadistis in their answer below  the original benchmarks that were used to determine the performance of the four methods described above were flawed  The original benchmark reused the cleared array so the second iteration was clearing an array that was already empty   The following benchmark fixes this flaw  http   jsben ch   hyj65  It clearly shows that methods  2  length property  and  3  splice  are the fastest  not counting method  1 which doesn t change the original array      This has been a hot topic and the cause of a lot of controversy  There are actually many correct answers and because this answer has been marked as the accepted answer for a very long time  I will include all of the methods here  If you vote for this answer  please upvote the other answers that I have referenced as well

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There is a lot of confusion and misinformation regarding the while pop shift performance both in answers and comments  The while pop solution has  as expected  the worst performance  What s actually happening is that setup runs only once for each sample that runs the snippet in a loop  eg   var arr        for  var i   0  i  lt  100  i           arr push Math random         for  var j   0  j  lt  1000  j          while  arr length  gt  0            arr pop       this executes 100 times  not 100000           I have created a new test that works correctly    http   jsperf com empty-javascript-array-redux  Warning  even in this version of the test you can t actually see the real difference because cloning the array takes up most of the test time  It still shows that splice is the fastest way to clear the array  not taking    into consideration because while it is the fastest it s not actually clearing the existing array

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The answers that have no less that 2739 upvotes by now are misleading and incorrect   The question is   How do you empty your existing array   E g  for A    1 2 3 4     Saying  A      is the answer  is ignorant and absolutely incorrect           is false   This is because these two arrays are two separate  individual objects  with their own two identities  taking up their own space in the digital world  each on its own      Let s say your mother asks you to empty the trash can     You don t bring in a new one as if you ve done what you ve been asked for  Instead  you empty the trash can   You don t replace the filled one with a new empty can  and you don t take the label  A  from the filled can and stick it to the new one as in A    1 2 3 4   A         Emptying an array object is the easiest thing ever   A length   0    This way  the can under  A  is not only empty  but also as clean as new      Furthermore  you are not required to remove the trash by hand until the can is empty  You were asked to empty the existing one  completely  in one turn  not to pick up the trash until the can gets empty  as in   while A length  gt  0        A pop       Nor  to put your left hand at the bottom of the trash  holding it with your right at the top to be able to pull its content out as in   A splice 0  A length      No  you were asked to empty it   A length   0    This is the only code that correctly empties the contents of a given JavaScript array

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Use a modified version of Jan s initial suggestion  var originalLength   A length  for  var i   originalLength  i  gt  0  i--         A pop       Terser  for  let i   A length  i  gt  0 A pop   i--      Or here s another take  while  A Symbol iterator    next   done A shift

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You can add this to your JavaScript file to allow your arrays to be  cleared    Array prototype clear   function         this splice 0  this length        Then you can use it like this   var list    1  2  3   list clear      Or if you want to be sure you don t destroy something   if   Array prototype clear        Array prototype clear   function            this splice 0  this length              Lots of people think you shouldn t modify native objects  like Array   and I m inclined to agree  Please use caution in deciding how to handle this

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A more cross-browser friendly and more optimal solution will be to use the splice method to empty the content of the array A as below   A splice 0  A length

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A splice 0    I just did this on some code I am working on   It cleared the array

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If you use constants then you have no choice   const numbers    1  2  3    You can not reasign   numbers        You can only truncate   numbers length   0

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I m surprised no one has suggested this yet   let xs    1 2 3 4   for  let i in xs      delete xs i     This yields an array in quite a different state from the other solutions  In a sense  the array has been  emptied    xs   gt  Array    lt 4 empty slots gt         xs    gt  Array   undefined  undefined  undefined  undefined    xs length   gt  4  xs 0    gt  ReferenceError  reference to undefined property xs 0    You can produce an equivalent array with        or Array 4

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Here the fastest working implementation while keeping the same array   mutable     function clearArray array      while  array length        array pop            FYI it cannot be simplified to while  array pop     the tests will fail   FYI Map and Set define clear    it would have seem logical to have clear   for Array too   TypeScript version   function clearArray lt T gt  array  T        while  array length        array pop            The corresponding tests   describe  clearArray          gt      test  clear regular array        gt        const array    1  2  3  4  5       clearArray array       expect array length  toEqual 0       expect array 0   toEqual undefined       expect array 4   toEqual undefined            test  clear array that contains undefined and null        gt        const array    1  undefined  3  null  5       clearArray array       expect array length  toEqual 0       expect array 0   toEqual undefined       expect array 4   toEqual undefined               Here the updated jsPerf  http   jsperf com array-destroy 32 http   jsperf com array-destroy 152

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Array prototype clear   function         this length   0       And call it  array clear

[javascript] How do I empty an array in JavaScript?

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