"Turn" a typical JavaScript face question

Issue 1: scope (SCOPE)

1 (function() {2   "use strict"; 3   var a = b = 5; 4 })(); 5 Console.log (b);

What does the console print?

Answer:

The above code will print out 5 .

The pitfall of this problem is that there are two assignments in the immediate execution function expression (iife), but the variables are a declared using keywords var . This means that it a is a local variable of the function. In contrast, it b is assigned to the global scope (that is, the global variable).

Another pitfall of this problem is that "strict mode" () is not used in the function ‘use strict‘; . If strict mode is turned on, then the code will error "uncaught referenceerror:b is not defined". Keep in mind that if this is the expected behavior, strict mode requires that you explicitly refer to the global scope. So, you need to write like this:

1 (function  () {2   ' use strict '; 3   var a = b = 5; 4 }) (); 5 Console.log (b);

Note: In strict mode, Firefox is still output 5, and 360 browser only error is "uncaught referenceerror:b are not defined".

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