# 1.2.3.6.函數陳述句與函數表示式

* 表達式 (expression)
  * 程式碼的單位, 最終會形成一個值
* 函數陳述句 
  * 不會回傳值, 但是會做特別的事如[hoisting](https://jenhsuan.gitbooks.io/javascript-node-js/content/chapter1/121zhi-xing-huan-jing-yu-ci-hui-huan-jing/1212zhi-xing-huan-jing-ff1a-chuang-zao-yu-ti-sheng.html), **在執行環境的創造階段就會將函數放進記憶體中**
* 將函數給另一個函數使用, 是**函數程式語言 (functional programming)**的概念

```
//表達式
var a;
a = 3;
1 + 2;
a = {greeting: 'hi'}

//if陳述句 
if (a == 3){
}

//函數陳述句: 不會回傳值
greet();

function greet() {
    console.log('hi');
}

//函數表達式: 變數將會指向記憶體的位置, 因為函數在宣告就已經在記憶體中佔有位置了

//執行會失敗, 因為anonymousGreet在執行階段才會被賦值, 此時還是undefined
//函數表達式沒有被提升
anonymousGreet();

var anonymousGreet =  function() {
    console.log('hi');
}

//執行成功
anonymousGreet();

function log(a){
    console.log(a);
}

//印出3
log(3);

//印出Hello
log("Hello")

//印出Object {greeting: "hi"}
log({greeting: 'hi'})

//將函數放到函數的CODE property
//印出function() {
//    console.log('hi');
//}

log(function() {
    console.log('hi');
})

//使用傳入的函數
//印出'hi'
function log(a){
    a();
}

log(function() {
    console.log('hi');
})
```

![](/files/-M4M0MvZ44mou9d5cu6f)


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