How to Format Numbers by Prepending 0 to Single-Digit Numbers

[7, 7.5, -7.2345].forEach(myNumber => {
  let formattedNumber = myNumber.toLocaleString('en-US', {
    minimumIntegerDigits: 2,
    useGrouping: false
  })
  console.log(
    'Input:    ' + myNumber + '\n' +
    'Output:   ' + formattedNumber
  )
})

PHP prepend leading zero before single digit number, on-the-fly

You can use sprintf: http://php.net/manual/en/function.sprintf.php

<?php
$num = 4;
$num_padded = sprintf("%02d", $num);
echo $num_padded; // returns 04
?>

It will only add the zero if it's less than the required number of characters.

Edit: As pointed out by @FelipeAls:

When working with numbers, you should use %d (rather than %s), especially when there is the potential for negative numbers. If you're only using positive numbers, either option works fine.

For example:

sprintf("%04s", 10); returns 0010

sprintf("%04s", -10); returns 0-10

Where as:

sprintf("%04d", 10); returns 0010

sprintf("%04d", -10); returns -010

How to output numbers with leading zeros in JavaScript?

NOTE: Potentially outdated. ECMAScript 2017 includes String.prototype.padStart.

You'll have to convert the number to a string since numbers don't make sense with leading zeros. Something like this:

function pad(num, size) {
    num = num.toString();
    while (num.length < size) num = "0" + num;
    return num;
}

Or, if you know you'd never be using more than X number of zeros, this might be better. This assumes you'd never want more than 10 digits.

function pad(num, size) {
    var s = "000000000" + num;
    return s.substr(s.length-size);
}

If you care about negative numbers you'll have to strip the - and read it.

How to pad single-digit numbers with a leading 0

<?php foreach (range(1, 12) as $month): ?>
  <option value="<?= sprintf("%02d", $month) ?>"><?= sprintf("%02d", $month) ?></option>
<?php endforeach?>

You'd probably want to save the value of sprintf to a variable to avoid calling it multiple times.

Formatting a number with leading zeros in PHP

Use sprintf :

sprintf('%08d', 1234567);

Alternatively you can also use str_pad:

str_pad($value, 8, '0', STR_PAD_LEFT);

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