Replace Method not working correctly?

JavaScript
#1

function pairElement(str) {
var array = str.split(“”)

var array2D = array.map((single) =>
single
.replace(/A/,“A,T”)
.replace(/T/,“T,A”)
.replace(/C/,“C,G”)
.replace(/G/,“G,C”)
.split()
);
console.log(str)
console.log(array)
return array2D;
}

console.log(pairElement(“ATCG”));

console shows:
ATCG
[ ‘A’, ‘T’, ‘C’, ‘G’ ]
[ [ ‘A,T,A’ ], [ ‘T,A’ ], [ ‘C,G,C’ ], [ ‘G,C’ ] ]

I would like to have the 2D array show only 2 letters per inner array. My syntax is the same why are some arrays containing 2 while others contain three?

#2

Think about this logically. You are first replacing every “A” with “A,T”. And then you are replacing every “T” with “T,A”. Do you see that you added a “T” in the first replace and now it is going to be replaced by “T,A” in the second replace? So a single “A” is going to end up as:

"A" -> "A,T" // after first replace
"A,T" -> "A,T,A" // after second replace
#3

Shaw! Thank you Bruce this helps a ton. I switched to only match the first letter. Fixed the issue! You ROCCK!