function greet(firstname, lastname, language){
console.log(firstname);
console.log(lastname);
console.log(language);
}
//印出:
//undefined
//undefined
//undefined
//因為hoisting的緣故, 參數會在執行環境被建立時被給予初始值undefined
greet();
//印出:
//'John'
//undefined
//undefined
greet('John');
//預設函數的寫法
//1.不是每個瀏覽器都支援的做法
function greet(firstname, lastname, language = 'en'){
console.log(firstname);
console.log(lastname);
console.log(language);
}
//2.預設參數的做法
function greet(firstname, lastname, language){
//如果language是undefined就會被強制轉型為false
language = language || 'en';
console.log(firstname);
console.log(lastname);
console.log(language);
}
function greet(firstname, lastname, language){
//如果language是undefined就會被強制轉型為false
language = language || 'en';
if (argements.length === 0){
return;
}
console.log(firstname);
console.log(lastname);
console.log(language);
console.log(argements);
}
//印出:
//'John'
//undefined
//undefined
//['John'] (array-like)
greet('John');