Passing an array as a function parameter in JavaScript

Question

I d like to call a function using an array as parameters   const x     p0    p1    p2    call me x 0   x 1   x 2       I don t like it  function call me  param0  param1  param2                  Is there a better way of passing the contents of x into call me

User · Accepted Answer

const args     p0    p1    p2    call me apply this  args     See MDN docs for Function prototype apply       If the environment supports ECMAScript 6  you can use a spread argument instead   call me    args

User · Answer

Note this  function FollowMouse         for var i 0  i lt  arguments length  i              arguments i  style top   event clientY  px           arguments i  style left   event clientX  px                 ---------------------------  html page   lt body onmousemove  FollowMouse d1 d2 d3   gt    lt p gt  lt div id  d1  style  position  absolute   gt Follow1 lt  div gt  lt  p gt   lt div id  d2  style  position  absolute   gt  lt p gt Follow2 lt  p gt  lt  div gt   lt div id  d3  style  position  absolute   gt  lt p gt Follow3 lt  p gt  lt  div gt     lt  body gt    can call function with any Args   lt body onmousemove  FollowMouse d1 d2   gt    or   lt body onmousemove  FollowMouse d1   gt

User · Answer

The answer was already given  but I just want to give my piece of cake  What you want to achieve is called method borrowing in the context of JS  that when we take a method from an object and call it in the context of another object  It is quite common to take array methods and apply them to arguments  Let me give you an example    So we have  super  hashing function which takes two numbers as an argument and returns  super safe  hashed string   function hash       return arguments 0      arguments 1      hash 1 2       1 2  whoaa   So far so good  but we have little problem with the above approach  it is constrained  only works with two numbers  that is not dynamic  let s make it work with any number and plus you do not have to pass an array  you can if you still insist   Ok  Enough talk  Let s fight   The natural solution would be to use arr join method   function hash       return arguments join       hash 1 2 4          Error  arguments join is not a function   Oh  man  Unfortunately  that won   t work  Because we are calling hash arguments  and arguments object is both iterable and array-like  but not a real array  How about the below approach   function hash       return    join call arguments      hash 1 2 3 4       1 2 3 4  whoaa   The trick is called method borrowing   We borrow a join method from a regular array    join  And use    join call to run it in the context of arguments   Why does it work   That   s because the internal algorithm of the native method arr join glue  is very simple   Taken from the specification almost    as-is      Let glue be the first argument or  if no arguments  then a comma      Let result be an empty string  Append this 0  to result  Append glue and this 1   Append glue and this 2      Do so until this length items are glued  Return result    So  technically it takes this and joins this 0   this 1     etc together  It   s intentionally written in a way that allows any array-like this  not a coincidence  many methods follow this practice   That   s why it also works with this arguments

User · Answer

Function arguments may also be Arrays   x000D   x000D  function foo  a b c   d     console log a b c d      foo  1 2 3   4  x000D   x000D   x000D   of-course one can also use spread   x000D   x000D  function foo a  b  c  d     console log a  b  c  d      foo     1  2  3   4  x000D   x000D   x000D

User · Answer

As  KaptajnKold had answered  var x      p0    p1    p2     call me apply this  x     And you don t need to define every parameters for call me function either  You can just use arguments  function call me             arguments is a array consisting of params         arguments 0      p0          arguments 1      p1          arguments 2      p2

User · Answer

While using spread operator we must note that it must be the last or only parameter passed  Else it will fail   function callMe    arr     valid arguments     alert arr      function callMe name     arr     valid arguments     alert arr      function callMe    arr  name     invalid arguments     alert arr       If you need to pass an array as the starting argument you can do   function callMe arr  name       let newArr       arr       alert newArr

User · Answer

Assuming that call me is a global function  so you don t expect this to be set   var x     p0    p1    p2    call me apply null  x

User · Answer

Why don t you pass the entire array and process it as needed inside the function   var x      p0    p1    p2      call me x    function call me params      for  i 0  i lt params length  i          alert params i

User · Answer

you can use spread operator in a more basic form     concat    array    in the case of functions that return arrays but are expected to pass as arguments  Example   function expectArguments    args     return    concat    args      JSON stringify expectArguments 1 2 3       JSON stringify expectArguments  1 2 3

User · Answer

In ES6 standard there is a new spread operator     which does exactly that   call me    x    It is supported by all major browsers except for IE   The spread operator can do many other useful things  and the linked documentation does a really good job at showing that

[javascript] Passing an array as a function parameter in JavaScript

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