javascript - 当我们使用模板文字时 `use strict` 不工作

Question

如果我用反引号/模板文字将 use strict 括起来，'use strict' 不会按预期工作。你能分享一下背后的原因吗？是否存在模板文字无法按预期工作的类似异常语句？

`use strict`;
x = 3.14;  // Ideally it should  cause an error (as x is not defined).
alert(x);

`use strict`; // if we enclose in single quotes or double quotes
x = 3.14;    // Ideally it should  cause an error (as x is not defined).
alert(x);

Answer 1

它就是这样设计的。

来自ES6 specification :

14.1.1 Directive Prologues and the Use Strict Directive

A Directive Prologue is the longest sequence of ExpressionStatement productions occurring as the initial StatementListItem or ModuleItem productions of a FunctionBody, a ScriptBody, or a ModuleBody and where each ExpressionStatement in the sequence consists entirely of a StringLiteral token followed by a semicolon. The semicolon may appear explicitly or may be inserted by automatic semicolon insertion. A Directive Prologue may be an empty sequence.

A Use Strict Directive is an ExpressionStatement in a Directive Prologue whose StringLiteral is either the exact code unit sequences "use strict" or 'use strict'. A Use Strict Directive may not contain an EscapeSequence or LineContinuation.

A Directive Prologue may contain more than one Use Strict Directive. However, an implementation may issue a warning if this occurs.

^{强调我的。}

它明确指出，为了使 Use Strict 指令起作用，它必须用单引号或双引号引起来，但模板文字根本不允许用于此目的。