How do I get the array I want from this for loop

I try unsuccessfully to get an array I wanted from this loop:

var a = [1,2,3,4];

var b = [];
for (var i = 0; i < 4; i++) {
   b.push(a[i]);
   console.log(b); // [1]
                           // [1, 2]
                           // [1, 2, 3]
                           // [1, 2, 3, 4]
}

Code (markup):

The result I wanted is:

[1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4]

Code (markup):

How do I get it?
Thank you,

Note: I don't want var c = a.concat(a,a,a); as data may different.

 

Hello,

I don't exactly understand why do you want to avoid using concat, but if you do, you can achieve this result using inner loop like this:

var a = [1,2,3,4];
var b = [];

for (var i = 0; i < 4; i++) {
        for (var j = 0; j < a.length; j++) {
                b.push(a[j]);
        }
        console.log(b.toString());
}

Code (markup):

will output:

"1,2,3,4"
"1,2,3,4,1,2,3,4"
"1,2,3,4,1,2,3,4,1,2,3,4"
"1,2,3,4,1,2,3,4,1,2,3,4,1,2,3,4"

Code (markup):

The resulting array is created by appending items one by one.

 

Thank you,
I do not avoid using concat but I don't want array a to repeat itself as it may different.
The array is generated by another function and it is feed into this function. Here's the mock up:

setInterval(function(){
   var a = Math.floor((Math.random()*100)+1);
   x(a);
},500);

function x(i) {
   this.i = i;
   console.log(i);
   
   var b = [];
   for (var i = 0; i < 4; i++) {
     // pick every 4 i's that reached here and put them together
   }
}

Code (markup):

I want to pick every 4 arrays from that serial to be merged together (concat) but I've no idea how to do it.
Hope, I explain it clearly.

 

So I believe you want this:

function x(input) {
        console.log(input);

        if(!this.counter) { // initialize the variables
                this.data = [];
                this.counter = 0;
        }

        // append this input to the rest
        this.data = this.data.concat(input);
        this.counter++;

        if(this.counter == 4) {
                // do something with the output
                output = this.data;
                console.log(output);

                // clear the data to repeat the cycle
                this.data = [];
                this.counter = 0;
        }
}

Code (markup):

This will wait for 4 input arrays and put them together.

 

Thank you so much.
You've saved me from pulling all my hair off.