(es/minifier): proposal of unsafe_Function_length

[Le0Developer]

Describe the feature

The idea boils down to not preserving the .length property of a function to enable:

• removing unused arguments from function definition
• putting variable declarations into the function definition

This would be a unsafe option.

Examples:

// input:
function helloWorld(unused) {
    console.log("Hello, World!")
}

helloWorld();
helloWorld(); // twice so it doesnt inline

// output:
function helloWorld(o){console.log("Hello, World!")}helloWorld(),helloWorld();
//                  ^ unused variable

// could be (saves 1 byte)
function helloWorld(){console.log("Hello, World!")}helloWorld(),helloWorld();

// input:
function foo() {
    var a = console.log.bind(console)
    a("Test 1")
    a("Test 2")
}

foo()
foo()

// output:
function foo(){var o=console.log.bind(console);o("Test 1"),o("Test 2")}foo(),foo();

// could be (saves 3 bytes)
function foo(o){o=console.log.bind(console);o("Test 1"),o("Test 2")}foo(),foo();

Potentially the assignment could also be done via default values, however I am not quite sure how safe this is.
For example:

// could be (saves 2 additional bytes)
function foo(o=console.log.bind(console)){o("Test 1"),o("Test 2")}foo(),foo();

Babel plugin or link to the feature description

No response

Additional context

Playground example

[kdy1]

It seems too risky compared to the gain