It works without $(document).ready, but not with it. Why?

Question

JavaScript

<div class="isMulti">
  <label class="container">
    <input type="radio" name="isMulti" value="single" checked="">
    <span class="point"></span>
  </label>
  <div>Single answer</div>
</div>
      
<div class="isMulti">
  <label class="container">
    <input type="radio" name="isMulti" value="multi">
    <span class="point"></span>
  </label>
  <div>Multi answer</div>
</div>

$(document).ready(function {
  $('.isMulti').click(function() {
    $(this).find('input').prop('checked', true);
  });
});

Answer 1

$(document).ready(function {
...

Not confused by the lack of parentheses after function ?

Answer 2

why checked=""?
you just need to write checked without any "="