text_table.js

test_data = [
    ['Source IP', 'Source Netmask', 'Destination IP', 'Destination Netmask', 'Port', 'Protocol', 'Action'],
	['123.456.789.000', '/30', '111.111.111.111', '/30', '8080', 'TCP', 'Accept'],
	['123.23.45.233', '/31', '127.0.0.1', '/8', '22', 'UDP', 'Deny'],
	['1.1.1.1', '/31', '1.2.3.4', '/30', '1', 'TCP', 'Deny'],
	['10.0.156.35', '/24', '123.32.234.7', '/12', '1337', 'BGP', 'Accept'],
];

// List<List<String>> -> String
// Assumes a non-empty list of non-empty lists of Strings
function create_table(lst){
    retVal = "";
    size = lst[0].length;
    spaces = [lst[0].length];
    num_dashes = 0;
    for(var x = 0; x < lst[0].length; x++){
        spaces[x] = 0;
    }
    
    //get spaces info
    for(var i = 0; i < lst.length; i++){
        tmp_dashes = 0;
        for(let y = 0; y < size; y++){
            tmp_dashes += lst[i][y].length;
            tmp = Math.floor(lst[i][y].length / 8) + 1;
            if(tmp > spaces[y]) {
                spaces[y] = tmp;
            }
            tmp = 1;
        }
        if(tmp_dashes > num_dashes){
            num_dashes = tmp_dashes;
        }
    }
    
    //add tab spaces to dashes
    for(var m = 0; m < spaces.length; m++) {
        num_dashes += spaces[m];
    }
    
    // start adding values to return String
    for(var i = 0; i < lst.length; i++){
        for(var y = 0; y < lst[i].length; y++) {
            retVal += lst[i][y];
            this_size = Math.floor(lst[i][y].length / 8);
            for(k = this_size; k < spaces[y]; k++) {
                retVal += '\t';
            }
        }
        retVal += '\n';
        
        // if after first row, add line of dashes
        if(i === 0) {
            for(var c = 0; c < num_dashes; c++){
                retVal += '-';
            }
            retVal += '\n';
        }
    }
    return retVal;
}


result = create_table(test_data);

console.log(result);