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JavaScript: Comma Operator

Description

The comma operator (,) is used to execute two expressions sequentially.

Syntax

expr1, expr2

Parameters

expr1: Any expressions.

expr2: Any expressions.

We use the comma operator when we want to include multiple expressions in a location that requires a single expression. This operator is generally used inside a for loop, to allow multiple variables to be updated (increase/decrease) each time through the loop.

For example, we want to display a serial No. (starting from 1) and an employee code ( starting from 10 ), the following code uses the comma operator to increment two variables at once.

for (var i=1, j=10; i <=10; i++, j++)
{
alert('Sl. No. : '+i+' Employee Code : '+j)
}

See also

Conditional Operator
delete
function
in
instanceof
new
this
typeof
void

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JavaScript: Tips of the Day

How to insert an item into an array at a specific index (JavaScript)?

What you want is the splice function on the native array object.

arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert). In this example we will create an array and add an element to it into index 2:

var arr = [];
arr[0] = "Jani";
arr[1] = "Hege";
arr[2] = "Stale";
arr[3] = "Kai Jim";
arr[4] = "Borge";

console.log(arr.join());
arr.splice(2, 0, "Lene");
console.log(arr.join());

Ref: https://bit.ly/2BXbp04