11. 函数

1. 默认值

// 例子 11-1
 
// bad
function test(quantity) {
  const q = quantity || 1;
}
 
// good
function test(quantity = 1) {
  ...
}

// 例子 11-2
 
doSomething({ foo: 'Hello', bar: 'Hey!', baz: 42 });
 
// bad
function doSomething(config) {
  const foo = config.foo !== undefined ? config.foo : 'Hi';
  const bar = config.bar !== undefined ? config.bar : 'Yo!';
  const baz = config.baz !== undefined ? config.baz : 13;
}
 
// good
function doSomething({ foo = 'Hi', bar = 'Yo!', baz = 13 }) {
  ...
}
 
// better
function doSomething({ foo = 'Hi', bar = 'Yo!', baz = 13 } = {}) {
  ...
}

// 例子 11-3
 
// bad
const Button = ({className}) => {
    const classname = className || 'default-size';
    return <span className={classname}></span>
};
 
// good
const Button = ({className = 'default-size'}) => (
    <span className={classname}></span>
);
 
// better
const Button = ({className}) =>
    <span className={className}></span>
}
 
Button.defaultProps = {
    className: 'default-size'
}

// 例子 11-4
 
const required = () => {throw new Error('Missing parameter')};
 
const add = (a = required(), b = required()) => a + b;
 
add(1, 2) // 3
add(1); // Error: Missing parameter.