jQuery到纯香草JS

Question

I'd like to convert this small script to a pure vanilla JS .

$('input, textarea').focus(function() { 
        $(this).data('placeholder', $(this).attr('placeholder')).attr('placeholder', '');
    }).blur(function() { 
            $(this).attr('placeholder', $(this).data('placeholder'));
});

DEMO

Thanks to Treast, I'm here at this point... Almost working good:

var elements = document.querySelectorAll('input, textarea');

for(var i = 0; i < elements.length; i++) {
    var element = elements[i];
    element.addEventListener('focus', function() {
        element.setAttribute('data-placeholder', element.getAttribute('placeholder'));
        element.setAttribute('placeholder', '');
    }),
  element.addEventListener('blur', function() {
        element.setAttribute('placeholder', element.getAttribute('data-placeholder'));
        element.setAttribute('data-placeholder', '');
    });
}

DEMO 2

Any idea please?

Answer 1

$('input, textarea') will select ALL input or textarea. With Vanilla, you cannot add an EventListener on a list of elements, so you need to loop through all elements. And you need to use querySelectorAll to get the same list. Also, you cannot chain addEventListener .

So your code will be:

var elements = document.querySelectorAll('input, textarea');

for(var i = 0; i < elements.length; i++) {
    var element = elements[i];
    element.addEventListener('focus', function() {
        this.setAttribute('data-placeholder', this.getAttribute('placeholder'));
        this.setAttribute('placeholder', '');
    });
    element.addEventListener('blur', function() {
        this.setAttribute('placeholder', this.getAttribute('data-placeholder'));
        this.setAttribute('data-placeholder', '');
    });
}

Answer 2

Have a good look at Patrick's comment above about if this is even needed.

--

As for converting your code to vanilla JS, I think the only issue with your Demo 2 is an unclosed Button tag. I'd suggest splitting things up to help readability. Have a look: https://jsfiddle.net/Lebxdrwk/2/

const onFocus = event => {
  const element = event.target;
  const placeholder = element.getAttribute('placeholder');
  element.setAttribute('data-placeholder', placeholder);
  element.setAttribute('placeholder', '');
};

const onBlur = event => {
  const element = event.target;
  const dataPlaceholder = element.getAttribute('data-placeholder');
  element.setAttribute('placeholder', dataPlaceholder);
  element.setAttribute('data-placeholder', '');
}

const addEventListenersToSwapPlaceholders = element => {
  element.addEventListener('focus', onFocus);
  element.addEventListener('blur', onBlur);
}

document.querySelectorAll('input, textarea')
  .forEach(addEventListenersToSwapPlaceholders);