CODEWITHSUNDEEP
javascriptarrays
m0j1
m0j1

Reputation: 4267

Javascript array with index in declaration

I'm running a js code and in some part of it there is a definition of an array which I don't get what it means , it looks like this :

var myArray = new Array();
myArray[myNum] = new Array();
myArray[myNum].push(value1);

I don't get why there is an index of the array at the second line , is it a two dimensional array ? I'll appreciate if you can help me with this.
thanks

Upvotes: 0

Views: 73

Answers (3)

MarsOne
MarsOne

Reputation: 2186

Let me try to explain your code....

Explanation:

var myArray = new Array();   // (1)
myArray[myNum] = new Array();  // (2)
myArray[myNum].push(value1);  // (3)

(1) This creates a new empty array . It could be 1D, 2D, 3D. Currently it has nothing. At this point you array should look like this..

myArray= [];

(2) This creates another empty Array in "myArray" at index "myNum". Let us assume myNum=5;

So

myArray[5] = new Array();

Will give

myArray =[[]];

(3) This will push value1 into myArray at index "myNum". Let us again assume myNum=5 and value1 = 1,2,3;

So

myArray[5].push(1,2,3);

Will give

myArray=[[1,2,3]]

DEMO IN A FIDDLE

Upvotes: 1

MD Sayem Ahmed
MD Sayem Ahmed

Reputation: 29166

var myArray = new Array();

Creates an array.

myArray[myNum] = new Array();

Creates an array in myArray's myNum index.

myArray[myNum].push(value1);

Stores valuea1 into the array (adds the element at the last, in this case at 0-th index) stored in myArray[myNum].

Yes, your assumption is right - after the execution of the three statements a two dimensional array is created, which looks something like this - 

[....., [value1], ......]  // the inner array is stored at "myNum" index

To access value1, you can now do - 

myArray[myNum][0];

See the doc for push.

Upvotes: 5

Mark Walters
Mark Walters

Reputation: 12390

This code just creates an array with an array at index myNum. Lets break the code down.

var myArray = new Array();
//Create a new array
myArray[myNum] = new Array();
//At index 'myNum' which is a variable presumably holding an index - create a new array
myArray[myNum].push(value1);
//push variable `value1` to the new array at index myNum of myArray.

Upvotes: 1

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