Javascript 中的符号及其示例

javascript
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// create unique symbols
const id = symbol('id');
const name = symbol('name');

// create an object with symbol-based properties
const user = {
    [id]: 101,
    [name]: 'alice',
    age: 25
};

// access the symbol properties
console.log(user[id]); // 101
console.log(user[name]); // "alice"

// add another property using a symbol
const email = symbol('email');
user[email] = 'alice@example.com';

console.log(user[email]); // "alice@example.com"

// symbols are not enumerable in for...in loops or object.keys
for (const key in user) {
    console.log(key); // only "age" is logged
}

console.log(object.keys(user)); // ["age"]

// you can still access all properties if you know the symbol keys
console.log(object.getownpropertysymbols(user)); // [symbol(id), symbol(name), symbol(email)]

javascript
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const collection = {
    items: ['apple', 'banana', 'cherry'],
    [symbol.iterator]() {
        let index = 0;
        const items = this.items;
        return {
            next() {
                if (index < items.length) {
                    return { value: items[index++], done: false };
                } else {
                    return { done: true };
                }
            }
        };
    }
};

// iterate over the object
for (const item of collection) {
    console.log(item);
}
// output:
// apple
// banana
// cherry

javascript
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// In Express.js, a symbol is used to define a unique property key
const app = express();
app[Symbol('router')] = router;