如何使用“严格模式”保护我的JavaScript？
“usestrict”是一条指令，它是一个文字表达。它在JavaScript1.8.5中引入。顾名思义，“使用严格”表示代码将在严格模式下执行。
让我们声明严格模式。要声明，请在开头添加关键字“usestrict”。对于全局作用域，请在脚本开头声明它。
示例
<!DOCTYPE html>
<html>
<body>
<p>An error would come, since you have used a variable, but forgot to declare it</p>
<p>Press F8 to see the error.</p>
<script>
"use strict";
a = 1;
</script>
</body>
</html>输出结果
An error would come, since you have used a variable, but forgot to declare it Press F8 to see the error.