Truncate String  字符串删节（截取）

截断字符串到指定的长度

const truncateString = (str, num) =>
  str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;

举个例子：

var str = "Apache Ant is a Java based build tool from Apache Software Foundation.";

truncateString(str, 30);

输出：

"Apache Ant is a Java based ..."