Add leading zeroes to number in Dart
<p>I want to add some leading zeroes to a string. For example, the total length may be eight characters. For example:</p>

<pre><code>123 should be 00000123
1243 should be 00001234
123456 should be 00123456
12345678 should be 12345678
</code></pre>

<p>What is an easy way to do this in Dart?</p>