# 【emit】

我們可以寫一個函數裡面加上 `emit` 這個動詞來觸發事件。

舉例來說：如果我們先建立事件並且於函數裡觸發它。

```solidity
pragma solidity ^0.8.11;

contract Test {
   event Deposit(address indexed _from, bytes32 indexed _id, uint _value);
   function deposit(bytes32 _id) public payable {      
      emit Deposit(msg.sender, _id, msg.value);
   }
}
```

後在 Javascript 使用 web3.js 的套件呼叫合約事件，web3.js 在之後的章節會特別介紹！

```javascript
var abi = /* abi as generated using compiler */;
// 要使用合約內容必須要得到合約在 compiler 之後輸出的 abi
var ClientReceipt = web3.eth.contract(abi);
var clientReceiptContract = ClientReceipt.at("0x1234...ab67" /* address */);

// 呼叫事件 Deposit：
var event = clientReceiptContract.Deposit(function(error, result) {
   if (!error)console.log(result);
});
```

在前端（dapp）回傳的結果如下：

```javascript
{
   "returnValues": {
      "_from": "0x1111...FFFFCCCC",
      "_id": "0x50...sd5adb20",
      "_value": "0x420042"
   },
   "raw": {
      "data": "0x7f...91385",
      "topics": ["0xfd4...b4ead7", "0x7f...1a91385"]
   }
}
```

如果我們今天輸入 `0x05416460deb76d57af601be17e777b93592d8d4d4a4096c57876a91c84f4a712` 也可以直接在 Remix 的下方互動環境看見一些資訊，包含 `logs` 等：

```javascript
logs = 
[
	{
		"from": "0x9DD41ECd6e1701CE34523ed98423c1eFb0805aBD",
		"topic": "0x19dacbf83c5de6658e14cbf7bcae5c15eca2eedecf1c66fbca928e4d351bea0f",
		"event": "Deposit",
		"args": {
			"0": "0x5B38Da6a701c568545dCfcB03FcB875f56beddC4",
			"1": "0x05416460deb76d57af601be17e777b93592d8d4d4a4096c57876a91c84f4a712",
			"2": "0",
			"_from": "0x5B38Da6a701c568545dCfcB03FcB875f56beddC4",
			"_id": "0x05416460deb76d57af601be17e777b93592d8d4d4a4096c57876a91c84f4a712",
			"_value": "0"
		}
	}
]
```

接下來我們會一一介紹 `indexed`, `data`, `topics` 等專有名詞。


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