javascript - 将 javascript 数组从 0 切片到 Arrays.length 的目的是什么？

Question

我正在尝试从 ionic codePen 中理解源代码: http://codepen.io/ionic/pen/rxysG 开发人员在他的演示中使用了以下代码:

 $scope.messages = messageOptions.slice(0, messageOptions.length);

开发者为什么不写:

$scope.messages = messageOptions;   //messageOptions is an array defined in the code which you can check from the codepen link that I have pasted.

Answer 1

语句 $scope.messages = messageOptions.slice(0, messageOptions.length); 创建数组的克隆/副本并将其分配给 $scope.messages

你也可以用

 $scope.messages = messageOptions.slice();

演示代码

var messageOptions = [1, 2];
var messages = messageOptions.slice(0, messageOptions.length);

//Update 
messageOptions[0] = 100;

snippet.log("messages: " + JSON.stringify(messages));
snippet.log("messageOptions: " + JSON.stringify(messageOptions));

<!-- Provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>