input 输入框如何实现当光标聚焦时部分文字被选中

<input id="i" type="text" value="One two three">
 
$(document).ready(function(){
 
    $("#i").on("click",function(){
        var input = document.getElementById("i"),val = input.value;
        var click_position = getPosition(input);
         
        var start = val.lastIndexOf(" ",click_position);
        if(start == -1) start = 0;
        var end = val.indexOf(" ",click_position);
        if(end == -1) end = val.length;
     
        setSelection(input,start,end);
    });
 
     
    function setSelection(input, startPos, endPos) {
        input.focus();
        if (typeof input.selectionStart != "undefined") {
            input.selectionStart = startPos;
            input.selectionEnd = endPos;
        } else if (document.selection && document.selection.createRange) {
            input.select();
            var range = document.selection.createRange();
            range.collapse(true);
            range.moveEnd("character", endPos);
            range.moveStart("character", startPos);
            range.select();
        }
    }
    function getPosition (input) {
  var pos = 0;
  if (document.selection) {
    input.focus ();
    var selection = document.selection.createRange ();
    selection.moveStart ('character', -input.value.length);
    pos = selection.text.length;
  }
  else if (input.selectionStart || input.selectionStart == '0')
    pos = input.selectionStart;
  return pos;
}
     
})