Inconsistent result

[yype]

Hi there, the POC below outputs differently on mujs than on v8/jsc/chakracore.

function a() {
    b = [, 1]
    a = function() {
        return b
    }
    return a()
}
console.log(a())
a().shift()
console.log(a())

> d8 ./poc.js
,1
1

> ch ./poc.js
,1
1

> mujs ./poc.js
,1
,1

This POC seems to represent the root cause of a larger program hanging on mujs but not on v8/jsc/chakracore.
Thanks.

[dankox]

This is interesting problem. It seems like MuJS doesn't assign function name as variable in scope, because if you create the a function using var a = function() { then it works in the same way as all the others. Or maybe it's just different handling for "function expression" and "function declaration".

[ccxvii]

MuJS treats the current function name "a" as a local variable.

Assigning to "a" changes the local variable, instead of setting a global variable. Therefore the second and third calls to a() are still calling the original function, rather than the anonymous inner function.

[ccxvii]

The core issue here is how the difference between function declarations (statements) and function expressions work with binding the function name. For expressions, the binding is a local immutable binding. For declarations, the binding is in the outer scope. MuJS gets both of these wrong...

Example 1:

var a = function a(n) {
    a = 5
    console.log(1, a)
}
a()
console.log(2, a)

Example 2:

function b(n) {
    b = 5
    console.log(1, b)
}
b()
console.log(2, b)