⚖️attributes vs. properties

HTML attributes vs. DOM properties

🔸 HTML attributes ┊ DOM properties┊ attr-prop sync ┊

For element nodes, most standard HTML attributes automatically become properties of DOM objects. 📗 JS.info ⟩ Attributes and properties

<body id="page"> => body.id="page"

HTML attributes

attribute name is case-insensitive.
attribute values are always strings.
element.attributes collection is iterable and has all the attributes as objects with name and value properties.

codepen ⟩ HTML attributes
⬆️ 需要： $(), $all(), elem.attr()

📁 HTML

<div id="div" about="Elephant">DIV</div>

📁 JS

const {log} = console;
const div = $('div');

// ⭐️ attribute name is case-insensitive
log(div.attr('About')); // Elephant
log(div.attr('ABOUT')); // Elephant
log(div.attr('AboUt')); // Elephant

// ⭐️ set new attribute test="123"
div.attr('Test', 123);  // <div id='div' about='Elephant' test='123'>DIV</div>

// ⭐️ Note: div.attributes is NOT an array.
for (let attr of div.attributes) {
  log(`${attr.name} = ${attr.value}`);
}
// about = Elephant
// test = 123

DOM properties

DOM properties are NOT always strings. for example:
- input.checked (boolean)
- div.style (CSSStyleDeclaration)
a.href is always a full URL. ( 👉🏻 See: 💈範例 )

/* -------- helper -------- */

// show element's attribute & property
function showAttrProp(elem, attr, prop=attr){
  log(`${elem.nodeName.toLowerCase()}.${prop} = ${elem[prop]}`);
  log(`${attr}='${elem.attr(attr)}'`);
}

/* -------- ⭐️ `a.href` is always a full URL -------- */

const a = $('a');

showAttrProp(a, 'href');
// a.href = 'https://...#hello'     // ⭐️ full URL
// href='#hello'

property ⇔ attribute sync

standard attribute changes ⇒ auto-update property, and vice versa.
⭐️ with some exceptions ( 👉🏻 💈範例 )

codepen ⟩ input.value => value="..." not synced
⬆️ 需要： $(), $all(), elem.attr()

📁 HTML

<input>

📁 JS

const {log} = console;
let input = $('input');

/* -------- ⭐️ input.value => value="..." NOT synced -------- */
// input.value => user's current input
// input.defaultValue => value="..." (attribute)

// (介面)  ╱‾‾‾‾‾‾‾‾‾‾‾ ✅ ‾‾‾‾‾‾‾‾‾‾‾‾‾⤵︎
// input.attr('value', 'hi')    input.value = 'hi'
//         ↖___________ ❌ _____________╱  (裡面)

// input.attr('value') =✅=> input.value
input.attr('value', 'hi');
show();                         // input.value = 'hi' ✅ synced
                                // <input value='hi'> 

// input.value =❌=> attribute
input.value = 'what?';
show();                         // input.value = 'what?'
                                // <input value='hi'> ❌ NOT synced

// show input's attribute & property
function show(){
  log(`input.value = '${input.value}'`);
  log(input.outerHTML);
}

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Last updated 1 year ago