Prevent inputting leading 0

Question

I can input

0 but not 0123. How do I prevent users not to input 0 at the first position of the input text field?

Allow the zero, but trim it prior to using the value. See http://stackoverflow.com/q/6676488 — Robert Harvey, Oct 28 '14 at 03:46
Have you consider using ``? The advantage would be that you whould have access to `input.valueAsNumber` in most browsers — Endless, Oct 28 '14 at 14:04

Mark Reed · Accepted Answer · 2014-10-28T03:59:09.057

5

Let them input it, just trim it when focus changes:

inputElement.onblur = function() {
  this.value = this.value.replace(/^0+(?=\d)/,'');
}

Fiddle

Note that it's specifically looking for a digit (\d) after the 0's that it's nuking, so it won't touch the zero in something like 0.123. If you want to get rid of those, too, just change the \d to ., which matches any character whatsoever.

edited Oct 28 '14 at 03:59

answered Oct 28 '14 at 03:53

Mark Reed

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thanks for your answer but what I wanted is to prevent the user, like onkeypress. Is there a way? – mengmeng Oct 28 '14 at 04:54
There's a way to do almost anything. :) In this case it would be more complicated code and probably more confusing for the user, though. – Mark Reed Oct 28 '14 at 11:20
I have to agree with you on that! Thanks for your help :D – mengmeng Oct 30 '14 at 00:37

Rahul Desai · Answer 2 · 2014-10-28T04:13:41.390

One way to do this is to check the first character in the input using charAt().

Demo

JS:

function check(){
    var number = document.getElementById('input').value;
    if(number.charAt(0) === 0)
        alert('Leading zero in the input.')
    else
        alert('No leading zero in the input.')
}

EASIER SOLUTION:

For the input, just check the first character like an array:

if(number[0] === '0')
        // do something

Demo

Prevent inputting leading 0

2 Answers2