JavaScript: How do I avoid an "undefined" error when assigning object property values to an array?

Question

Currently receiving an undefined error when attempting to assign property values to a collection of objects.

Code:

MyArray = []; 
for(let j=0; j<5; j++) {
    MyArray[j].randoAttribute = 2;
    MyArray[j].anotherRandoAttrbute = 3;
}

Error message:

TypeError: Cannot set properties of undefined (setting 'randoAttribute')

Goal: How do I avoid this error and still be able to dynamically assign property values in an iterator?