how to determine if the browser supports selectionStart if there is no text selected

This code will return true if the browser supports selectionStart and some text is selected, but if no text is selected it returns false (even on brows开发者_如何学JAVAers that support it):

   if (el.selectionStart) {

  }

How do you determine if the property is available regardless of whether text happens to be selected?

Thanks

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Further googling revealed the answer:

 if (el.selectionStart != undefined) {

 }

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Hopefully this will help you. I tested it on an old Android 4.2 (which returns false) and Chrome (which returns true).

function selectionSupport() {
    var input = document.createElement("input");
    input.setAttribute('value', '111');
    input.selectionStart = 1;
    input.selectionEnd = 2;
    return (input.selectionStart === 1 && input.selectionEnd === 2);
}

var selectionIsSupported = selectionSupport();