forEach array javascript incomplete

Question

UPDATED

I am trying to build an array by calling a callback function and feeding it with values from other arrays. However, I get only few values and I cannot understand why.

the structure is like:

var sortedData = [];

arrayProvidingTheValues.forEach(pushEl,sortedData);

and the callback function is

function pushEl(element,index) {
   console.log("pushEl called");
   this[index] = element;
}

input:

saisineArray = {obj1, obj2 obj3, obj4, obj5, obj6};
contratArray = {obj21, obj22 obj23, obj24, obj25, obj26};
intervalNb = 5;

expected output

 sortedData = {obj1, obj2 obj3, obj4, obj5, obj6,obj21, obj22 obj23, obj24, obj25,obj6,obj26};

PS: this is the detailled code to show you in more detail.

for (var k = 0; k < intervalNb; k++) {
    if (k * interval >= saisineArray.length) {
    } else if ((k + 1) * interval >= saisineArray.length) {
        saisineArray.slice(k * interval, saisineArray.length).forEach(pushEl, sortedData);
    } else {
        saisineArray.slice(k * interval, (k + 1) * interval).forEach(pushEl, sortedData);
    }
    if (k * interval >= contratArray.length) {
    } else if ((k + 1) * interval >= contratArray.length) {
        contratArray.slice(k * interval, contratArray.length).forEach(pushEl, sortedData);
    } else {
        contratArray.slice(k * interval, (k + 1) * interval).forEach(pushEl, sortedData);
    }
}

Answer 1

Instead of this[index] = element; try this.push(element);

What you're doing now is on every execution of forEach(pushEl) you are overwriting the sortedData array starting from index 0.