js+调用+tostring

// 内置类型的 toString 方法
let num = 123;
console.log(num.toString()); // "123"

let bool = true;
console.log(bool.toString()); // "true"

let arr = [1, 2, 3];
console.log(arr.toString()); // "1,2,3"

let date = new Date();
console.log(date.toString()); // 例如 "Wed Oct 06 2021 12:34:56 GMT+0800 (China Standard Time)"

// 自定义类型的 toString 方法
function Person(name, age) {
    this.name = name;
    this.age = age;
}

Person.prototype.toString = function() {
    return `Person { name: ${this.name}, age: ${this.age} }`;
};

let person = new Person("Alice", 30);
console.log(person.toString()); // "Person { name: Alice, age: 30 }"

let value;
if (value !== undefined && value !== null) {
    console.log(value.toString());
} else {
    console.log("Value is undefined or null");
}

function CustomObject(data) {
    this.data = data;
}

CustomObject.prototype.toString = function() {
    // 确保这里的逻辑是正确的
    return `CustomObject { data: ${JSON.stringify(this.data)} }`;
};