HTMLElement.blur()

element.blur();

<input type="text" id="myText" value="Sample Text">
<br><br>
<button type="button" onclick="focusInput()">Click me to gain focus</button>
<button type="button" onclick="blurInput()">Click me to lose focus</button>

function focusInput() {
  document.getElementById('myText').focus();
}
function blurInput() {
  document.getElementById('myText').blur();
}