You should generate an array on every row iteration and output it at the end:
function generatePyramid() {
var totalNumberofRows = 5,
arr;
for (var i = 1; i <= totalNumberofRows; i++) {
arr = [];
for (var j = 1; j <= i; j++) {
arr.push(j);
}
console.log(arr.join(" ") + "\n");
}
}