Template Strings. Default Parameters. Concise Objects

Template Strings

• String的串接以往都是用 '+' 來連接

function makeGreeting (name, email, id) {
  return 'Hello, ' + name + '. We\'ve emailed you at ' + email '. Your user id is ' + id + '.'
}

• 可以改用如下的Template String就可以不用寫 '+'，而且(\')也可以拿掉escape character直接寫(')，但括起字串的就不是( ' )而是( ` )，而且變數要用(${})包起來。

function makeGreeting (name, email, id) {
  return `Hello, ${name}. We've emailed you at ${email}. Your user id is ${id}.`
}

Default Parameters

• 在function中當某個參數未定義時可能會想給一個預設值，以往會用下列寫法

function debounce (func, wait, immediate) {
  if (typeof wait === 'undefined') {
    wait = 1000
  }
  ...
}

• 但用Default Parameters的話可以更簡潔

function debounce (func, wait = 1000, immediate) {
 ...
}

Concise Objects

• 下面例子的function回傳一個物件

function getUser (username) {
  const email = getEmail(username)
  return {
    username: username,
    email: email
  }
}

• 上面那種名稱相同的情況可以用concise object簡化

function getUser (username) {
  const email = getEmail(username)
  return {
    username,
    email
  }
}