What is the way of declaring an array in JavaScript

Question

I m just learning JavaScript and it seems like there are a number of ways to declare arrays    var myArray   new Array   var myArray   new Array 3  var myArray     apples    bananas    oranges   var myArray    3    What are their difference  and what are the preferred ways   According to this website the following two lines are very different   var badArray   new Array 10      creates an empty Array that s sized for 10 elements var goodArray   10               creates an Array with 10 as the first element      As you can see these two lines do two very different things  If you   had wanted to add more than one item then badArray would be   initialized correctly since Javascript would then be smart enough to   know that you were initializing the array instead of stating how many   elements you wanted to add    Is what the authors trying to say is Array 10  creates an array with precisely 10 elements and  10  creates an array of undefined size with the 0th element being 10  Or what does this mean

User · Answer

If you are creating an array whose main feature is it's length, rather than the value of each index, defining an array as var a=Array(length); is appropriate.

eg-

String.prototype.repeat= function(n){
    n= n || 1;
    return Array(n+1).join(this);
}

User · Answer

There are a number of ways to create arrays   The traditional way of declaring and initializing an array looks like this   var a   new Array 5      declare an array  a   of size 5 a    0  0  0  0  0       initialize each of the array s elements to 0   Or        declare and initialize an array in a single statement var a   new Array 0  0  0  0  0

User · Answer

In your first example  you are making a blank array  same as doing var x        The 2nd example makes an array of size 3  with all elements undefined    The 3rd and 4th examples are the same  they both make arrays with those elements   Be careful when using new Array     var x   new Array 10      array of size 10  all elements undefined var y   new Array 10  5      array of size 2   10  5    The preferred way is using the    syntax   var x          array of size 0 var y    10     array of size 1   1   var z          array of size 0 z 2    12      z is now size 3   undefined  undefined  12

User · Answer

The preferred way is to always use the literal syntax with square brackets  its behaviour is predictable for any number of items  unlike Array s  What s more  Array is not a keyword  and although it is not a realistic situation  someone could easily overwrite it   function Array     return        alert Array 1  2  3       An empty alert box   However  the larger issue is that of consistency  Someone refactoring code could come across this function   function fetchValue n        var arr   new Array 1  2  3        return arr n       As it turns out  only fetchValue 0  is ever needed  so the programmer drops the other elements and breaks the code  because it now returns undefined   var arr   new Array 1

User · Answer

To declare it   var myArr     apples    oranges    bananas      To use it   document write  In my shopping basket I have     myArr 0           myArr 1       and     myArr 2

[javascript] What is the way of declaring an array in JavaScript?

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