Why is this code fine:

var test = {
    fn1: function(_origin, _ponentType) {
        if(arguments.length > 1) throw "xx";
        // this strict is ok
        "use strict";

        var interface               = new Object(this);
    }
}

While this isn't

var test = {
    fn1: function(_origin, _ponentType) {
        // This strict throws SyntaxError
        "use strict";

        if(arguments.length > 1) throw "xx";
        var interface               = new Object(this);
    }
}

I know interface is reserved word in strict mode, but shouldn't both examples throw an error?

Why is this code fine:

var test = {
    fn1: function(_origin, _ponentType) {
        if(arguments.length > 1) throw "xx";
        // this strict is ok
        "use strict";

        var interface               = new Object(this);
    }
}

While this isn't

var test = {
    fn1: function(_origin, _ponentType) {
        // This strict throws SyntaxError
        "use strict";

        if(arguments.length > 1) throw "xx";
        var interface               = new Object(this);
    }
}

I know interface is reserved word in strict mode, but shouldn't both examples throw an error?

• javascript
• strict-mode

2 Answers 2

"use strict"; needs to be the first statement in a function (or in a script, if script-wide) to trigger strict mode; anywhere else, you may as well be writing "merry christmas";.

The first example doesn't actually enable strict mode. See https://developer.mozilla/en-US/docs/Web/JavaScript/Reference/Strict_mode#Invoking_strict_mode:

Strict mode applies to entire scripts or to individual functions. It doesn't apply to block statements enclosed in {} braces; attempting to apply it to such contexts does nothing.