首先介绍箭头函数最直观的用法，即用作匿名回调函数。
The first and most intuitive use for an arrow function would be as an anonymous callback.
还可以展开跟踪中的条目（单击名称左边的向右小箭头），查看函数的形式参数的值。
You can also expand an entry in a backtrace — click the little right arrow to the left of the name — to see the values of the function's formal arguments.
始终填充用此构造函数创建的箭头端帽。
The arrow end caps created with this constructor are always filled.
始终填充用此构造函数创建的箭头端帽。
The arrow end caps created with this constructor are always filled.
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