难以理解的代码:
const printAnimalDetails = animal => {
let result; // declare a variable to store the final value
// condition 1: check if animal has a value
if (animal) {
// condition 2: check if animal has a type property
if (animal.type) {
// condition 3: check if animal has a name property
if (animal.name) {
// condition 4: check if animal has a gender property
if (animal.gender) {
result = `${animal.name} is a ${animal.gender} ${animal.type};`;
} else {
result = "No animal gender";
}
} else {
result = "No animal name";
}
} else {
result = "No animal type";
}
} else {
result = "No animal";
}
return result;
};
console.log(printAnimalDetails()); // 'No animal'
console.log(printAnimalDetails({ type: "dog", gender: "female" })); // 'No animal name'
console.log(printAnimalDetails({ type: "dog", name: "Lucy" })); // 'No animal gender'
console.log(
printAnimalDetails({ type: "dog", name: "Lucy", gender: "female" })
); // 'Lucy is a female dog'
虽然这段代码可以正常执行，但是使用过多的if...else嵌套使得你的代码变得难以理解。
使用return改进
const printAnimalDetails = ({type, name, gender } = {}) => {
if(!type) return 'No animal type';
if(!name) return 'No animal name';
if(!gender) return 'No animal gender';
// Now in this line of code, we're sure that we have an animal with all //the three properties here.
return `${name} is a ${gender} ${type}`;
}
console.log(printAnimalDetails()); // 'No animal type'
console.log(printAnimalDetails({ type: dog })); // 'No animal name'
console.log(printAnimalDetails({ type: dog, gender: female })); // 'No animal name'
console.log(printAnimalDetails({ type: dog, name: 'Lucy', gender: 'female' })); // 'Lucy is a female dog'
是不是简单多了？
