Asked  7 Months ago    Answers:  5   Viewed   36 times

So I have an array of records retreived from a database. The array is in the format;


//And so on upto 10-20 rows

What's the best way of transferring this array over to my javascript code? I'd like the javascript to be able to loop through all of the records, and using the 'id' attribute, update the div with that id with some information.

My javascript code is in an external .js file, but i'm able to execute php code in the HTML code of my page. So I could do something like this:

In my_file.js:

var rows=New Array();

In HTML code:

<script type="text/javascript" src="js/my_file.js"></script>

<script type="text/javascript">
<? foreach ($rows as $row):?>
<? extract($row);?>
//And so on
<? endforeach;?>



I tend to use a JSON object for this:

  • On the server side, JSON encode your data: json_encode($data);
  • On the JavaScript side, I write a function that takes a JSON object as a parameter and unpack it.

When you unpack the object, you can print the array's contents into a <DIV> tag, or where ever you would like on the page (jQuery does a pretty sweet job of this).

Wednesday, March 31, 2021
answered 7 Months ago

I took some liberties, and don't really understand PHP so I made up those parts. Anyway, here's what I got:

    <style type="text/css">

    <script type="text/javascript">
var ids = new Array();
var use = new Array();
var ful = new Array();

ids[0] = "";
use[0] = "";
ful[0] = "";

ids[1] = 6;
use[1] = "bsmith";
ful[1] = "Buddy Smith";

ids[2] = 2;
use[2] = "lsmith";
ful[2] = "Libbie Smith";

ids[3] = 4;
use[3] = "asmith";
ful[3] = "Andy Smith";

        function Choice() {
            //x = document.getElementById("users");
            y = document.getElementById("selectUsers");

              //x.value = y.options[y.selectedIndex].text;
              document.getElementById("ids").value = ids[y.selectedIndex];
              document.getElementById("use").value = use[y.selectedIndex];
              document.getElementById("ful").value = ful[y.selectedIndex];

<form name="form1" method="post" action="">
<select id="selectUsers" name="users" onChange='Choice();'><option> </option>
<option value="1">bsmith</option>
<option value="2">lsmith</option>
<option value="3">asmith</option>
<p>ids <input type="text" id="ids" name="id" ></p>
<p>use <input type="text" id="use" name="username" ></p>
<p>ful <input type="text" id="ful" name="full_name" ></p>
Wednesday, March 31, 2021
answered 7 Months ago

Java 8 introduces a String.join(separator, list) method; see Vitalii Federenko's answer.

Before Java 8, using a loop to iterate over the ArrayList was the only option:

DO NOT use this code, continue reading to the bottom of this answer to see why it is not desirable, and which code should be used instead:

ArrayList<String> list = new ArrayList<String>();

String listString = "";

for (String s : list)
    listString += s + "t";


In fact, a string concatenation is going to be just fine, as the javac compiler will optimize the string concatenation as a series of append operations on a StringBuilder anyway. Here's a part of the disassembly of the bytecode from the for loop from the above program:

   61:  new #13; //class java/lang/StringBuilder
   64:  dup
   65:  invokespecial   #14; //Method java/lang/StringBuilder."<init>":()V
   68:  aload_2
   69:  invokevirtual   #15; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   72:  aload   4
   74:  invokevirtual   #15; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   77:  ldc #16; //String t
   79:  invokevirtual   #15; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   82:  invokevirtual   #17; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;

As can be seen, the compiler optimizes that loop by using a StringBuilder, so performance shouldn't be a big concern.

(OK, on second glance, the StringBuilder is being instantiated on each iteration of the loop, so it may not be the most efficient bytecode. Instantiating and using an explicit StringBuilder would probably yield better performance.)

In fact, I think that having any sort of output (be it to disk or to the screen) will be at least an order of a magnitude slower than having to worry about the performance of string concatenations.

Edit: As pointed out in the comments, the above compiler optimization is indeed creating a new instance of StringBuilder on each iteration. (Which I have noted previously.)

The most optimized technique to use will be the response by Paul Tomblin, as it only instantiates a single StringBuilder object outside of the for loop.

Rewriting to the above code to:

ArrayList<String> list = new ArrayList<String>();

StringBuilder sb = new StringBuilder();
for (String s : list)


Will only instantiate the StringBuilder once outside of the loop, and only make the two calls to the append method inside the loop, as evidenced in this bytecode (which shows the instantiation of StringBuilder and the loop):

   // Instantiation of the StringBuilder outside loop:
   33:  new #8; //class java/lang/StringBuilder
   36:  dup
   37:  invokespecial   #9; //Method java/lang/StringBuilder."<init>":()V
   40:  astore_2

   // [snip a few lines for initializing the loop]
   // Loading the StringBuilder inside the loop, then append:
   66:  aload_2
   67:  aload   4
   69:  invokevirtual   #14; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   72:  pop
   73:  aload_2
   74:  ldc #15; //String t
   76:  invokevirtual   #14; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   79:  pop

So, indeed the hand optimization should be better performing, as the inside of the for loop is shorter and there is no need to instantiate a StringBuilder on each iteration.

Tuesday, June 1, 2021
answered 5 Months ago

You should return the data as JSON from the server.


$arr = array();
$arr[0] = "Mark Reed";
$arr[1] = "34";
$arr[2] = "Australia";

echo json_encode($arr);


    type: "POST",
    url: "/returndetails.php",
    data: 'id=' + userid,
    dataType: "json", // Set the data type so jQuery can parse it for you
    success: function (data) {
        document.getElementById("name").innerHTML = data[0];
        document.getElementById("age").innerHTML = data[1];
        document.getElementById("location").innerHTML = data[2];
Wednesday, July 28, 2021
answered 3 Months ago

Call the constructor of Vector that uses an existing collection (your array, in this case) to initialize itself:

String[] strings = { "Here", "Are", "Some", "Strings" };
Vector<String> vector = new Vector<String>(Arrays.asList(strings));
Wednesday, August 11, 2021
answered 2 Months ago
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