Pascal's Triangle in JS

PascalsTriangle.js

/**
 * Generates Pascal's triangle
 * @param {number} numRows
 * @return {number[][]} Pascal's Priangle
 */
var generate = function(numRows) {
    var pascalsTriangle = [];
    
    //initial value at top of triangle
    if (numRows >= 1) {
        pascalsTriangle.push([1]);
    }
    
    //generate numRows rows
    for (var i = 1; i < numRows; i++) {
        // generate items in each Row
        var row = [];
        
        for (var j = 0; j < i + 1; j++) {
            var prevRow = pascalsTriangle[i - 1];
            var left = prevRow[j - 1] || 0;
            var right = prevRow[j] || 0;
            
            row.push(left + right);
        } 
        
        pascalsTriangle.push(row);
    }
    
    
    return pascalsTriangle;
};