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"use strict";
if (true) {
function foo() {
}
}
In PhpStorm this code shows an error:
Function statement not at top level of a program or function is prohibited
However, Chrome happily executes it, even in the debugger and without any console output.
Now is it prohibited or not?
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If you have such an unrestrictedly typed code, that is used variables without declaring. One variable declared within some function/scope and used from somewhere else(it will be undeclared there) and you can't rewrite/change them, then you should not go for "use strict;" mode because it will break the code.
Strict mode changes previously accepted "bad syntax" into real errors. As an example, in normal JavaScript, mistyping a variable name creates a new global variable. In strict mode, this will throw an error, making it impossible to accidentally create a global variable.
What is "use strict"; ? what are the advantages and disadvantages to using it? If you put "use strict"; at the top of your code (or function), then the JS is evaluated in strict mode. Strict mode throws more errors and disables some features in an effort to make your code more robust, readable, and accurate.
In strict mode all variables have to be declared: if you assign a value to an identifier that has not been declared as variable, function, function parameter, catch-clause parameter or property of the global Object , then you will get a ReferenceError .
Yes, in ES5 they are prohibited (and in strict mode, all implementations throw). See also Kangax' great article for function statements in sloppy mode.
However, in ES6 they are block-level function declarations with new semantics. See also What are the precise semantics of block-level functions in ES6?. This seems to be what Chrome implements here; foo is not available outside of the if block.
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