jquery - Sending an array from PHP to javascript

In the PHP file can anyone help me directly making a for loop where I don't know the number of rows that are going to be selected.

<?php
    $servername = "localhost";
    $username = "root";
    $password = "";
    $dbname = "mydb";//database details
    $conn = new mysqli($servername, $username, $password, $dbname);

    if ($conn->connect_error) 
    {
        die("Connection failed: " . $conn->connect_error);
    } 

    $sql = "SELECT * FROM mytable";
    $result = $conn->query($sql);
    $myarray = array();
    $index = 0;

    if ($result->num_rows > 0) 
    {
        // output data of each row
        while($row = $result->fetch_assoc()) 
        {
            $myarray[$index] = $row["firstname"];
            $index++;
            $myarray[$index] = $row["lastname"];
            $index++;
            $myarray[$index] = $row["email"];
            $index++;
        }
    } 
    else 
    {
        echo "0 results";
    }
    $conn->close();
?>
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The Javascript code contains javascript of a search bar suggestion code and here i didn't mention the typeahead javascript file

var substringMatcher = function(strs) {
    return function findMatches(q, cb) {
        var matches, substringRegex;

        // an array that will be populated with substring matches
        matches = [];

        // regex used to determine if a string contains the substring `q`
        substrRegex = new RegExp(q, 'i');

        // iterate through the pool of strings and for any string that
        // contains the substring `q`, add it to the `matches` array
        $.each(strs, function(i, str) {
            if (substrRegex.test(str)) {
                matches.push(str);
            }
        });

        cb(matches);
    };
};

$('#the-basics .typeahead').typeahead({
    hint: true, //here i used typeahead js code though i didnt mentioned here
    highlight: true,
    minLength: 1
}, {
    name: 'states',
    source: substringMatcher(states)
});
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