Remove side-effect free statements

[boopathi]

Input:

function foo() {
  a; 5; 6;
}

expected:

function foo() {}

[Rich-Harris]

Thinking about this, the low-hanging fruit would be any ExpressionStatement nodes whose expression is anything except a CallExpression, NewExpression, AssignmentExpression or UpdateExpression... does that sound about right?

There's also assignments to unused variables etc, but that's a little trickier, wasn't planning to tackle that just yet 😀

[boopathi]

Also,

• o.foo - getters
• instanceof - Symbol.hasInstance
• The tricky ones are a + "" a.toString is called. So all of arithmetic operators are to be treated as impure.

Edit:

• obj.valueOf