Basic

Selection

document.getElementById('myid');
document.getElementsByClassName('my-class');
document.getElementsByName('my-name');
document.getElementsByTagName('div');

document.querySelector('div.my-class');
document.querySelectorAll('div.my-class');

Edit

const el = document.getElementById('my-id');

el.getAttribute('src',);
el.setAttribute('src', 'https://example.com');

I think there is a cleaner way to do this with remove and no check, or toggle class.

// classList is now widely supported https://caniuse.com/#search=classList
if (el.classList.contains('my-class')) {
    el.classList.remove('my-class');
}

See video.

el.innerHTML = "<b>Hello</b>"

// Safe for security issues.
el.innerContent = "<b>Hello</b>"

el.innerText = "Hello"

Create list

<select id='my-id'></select>

const selectInput = document.getElementById('my-id');

for (let value of ['a', 'b', 'c']) {
    const option = document.createElement('option');
    option.setAttribute('value', value);
    option.text = value;
    selectInput.appendChild(option);
}