const input = document.querySelector('#input');

​

const format = /-?\d{0,5}(\.\d{0,2})?/;

let lastValue;

​

input.addEventListener('input', event => {

  document.execCommand('selectAll');

  let text = document.getSelection().toString();

  if (text !== lastValue) {

    const match = text.match(format);

    if (!match) {

      text = '';

    }

    else {

      text = match[0]

        .replace(/^(-?)0+(\d)/, '$1$2')

        .replace(/^(-?)\./, '$10.');

    }

    lastValue = text;

    document.execCommand('insertText', false, text);

  }

});