Function node code editor warnings

General
1

Are these warnings/errors displayed by the line numbers part of Node-RED's codebase, or is this functionality from another library?

The warnings/errors shown are wrong sometimes, e.g. defining a variable with var inside an if statement and then using it right after says it's out of scope (that would be true for let or const, not var).

2

It is the JavaScript parser that the ACE editor comes with.

I know it trips over some of the newer ES6 syntax.

Can you provide some specific examples?

3

This is within a function definition:

  // create request data
  if ([3, 4, 5, 6].includes(fc)) {
    var n = 2;
    var reqd = Buffer.from([(val >> 8) & 0xff, val & 0xff]);
  } else if (fc === 16) {
    const n_val = val.length;
    if (n_val > 127)
      throw 'Number of data values exceeds limit (127)';
    var n = 2*n_val + 3;
    var reqd = Buffer.concat([Buffer.from([0, n_val, 2*n_val]), ...val.map(x => Buffer.from([(x >> 8) & 0xff, x & 0xff]))]);
  } else
    throw 'Function code not implemented';

  // fill in message length
  n += 4;
  reqh[4] = (n >> 8) & 0xff;
  reqh[5] = n & 0xff;

  return Buffer.concat([reqh, reqd]);

It complains that n is already defined with at the 2nd "var n =" statement inside the else if (not true), complains @ fill in message length that n, reqh, and reqd are out of scope (not true, var is function scoped)

I've also used "== null" to test if something is null or undefined, and it gripes about how I need to use === to test against null. IMO it should say "be careful of the difference between == and ===" or something like that.

4

var is function scoped and you have used var n twice in this function.... so the error message is correct.

1 Like
5

The var n's are in different branches of an if statement, only one will be executed.

6

Doesn't matter. They are in the same function so will both get hoisted to the start of the function.

7

Touché, it appears you are correct. Oh goody, yet another JS quirk...I assumed that it worked like C/C++.

8

Never assume haha.

I mostly use let or const in block scope to avoid the side affects.