How can check the null or undefined values

General
1

How to determine if one variable of the payload is undefined or null in JavaScript then must not send it to DB.

2

In a function node, you could do something like:

if (typeof msg.payload.myVal != 'undefined' && msg.payload.myVal !== null) {
   return msg;
}

Or alternatively, you can use a switch node with the 'not null' condition.

2 Likes
3

Thank @kuema

4

Very often also NaN, +/-infinite cause problems. Therefore I use this small function:

isTruthy: input => {
    return !(typeof input === 'undefined' || input === null ||
      (typeof input === 'number' && !Number.isFinite(input)))
  },

... and for properties (example msg.payload.result --> isValidProperty(msg, ['paylaod', 'result']

isValidProperty: (nestedObj, pathArray) => {
    const property = pathArray.reduce(
      (obj, key) => (obj && obj[key] !== 'undefined' ? obj[key] : undefined),
      nestedObj
    )
    return isTruthy(property)
5

The value 'undefined' denotes that a variable has been declared, but hasn't been assigned any value. On the other hand, Javascript null refers to a non-existent object, which basically means 'empty' or 'nothing'. They're both values usually used to indicate the absence of something . Also, undefined and null are two distinct types: undefined is a type itself (undefined) while null is an object .

6

T9M2J
T9M2J1024Ă—768 186 KB

9 Likes
7

This works great for me,

if (typeof msg.payload.myVal != 'undefined') {
    msg.payload.myVal = 1;
}
return msg;

But, this does not,

if (typeof msg.payload.myVal != 'undefined') {
    msg.payload.myVal = 1;
} else {
    msg.payload.myVal = 0;
}
return msg;

The else never gets called when the condition isn't false.

If I change the != to == and reverse the if and the else blocks it still doesn't work, the else block simply doesn't get called.

My solution was the following:

msg.payload.myVal = 0;
if (typeof msg.payload != 'undefined') {
    msg.payload.myVal = 1;
}
return msg;

I have no idea why, but this information might help someone in the future.

Cheers!