Asking for assistance with understanding a particular line of JavaScript code

Can anyone explain the meaning of the "?" symbol in the JavaScript snippet provided below? The code is not wrapped for clarity, so I want to make sure I understand it correctly...

errMess = t.origStatus != undefined && t.status != t.origStatus && t.statuseffective == null ? errMess + t.systemname + ": Status effective date invalid.\n" : errMess;

In my interpretation:
errMess =
t.original status not equal to undefined AND
t.status not equal to original status AND
statuseffective equals null ? <-- unsure about this part

javascript

Answer №1

The concept being discussed here is a ternary operator.

This piece of code could alternatively be expressed as:

if (t.origStatus != undefined
     && t.status != t.origStatus
     && t.statuseffective == null) {
    errMess = errMess + t.systemname + ": Status effective date invalid.\n";
} else {
    errMess = errMess;
}

To clarify, X = A ? B : C can be understood as:

if (A) {
    X = B;
} else {
    X = C;
}

Here are some additional points to consider:

  • t.origStatus != undefined is essentially the same as t.origStatus != null, since in an equality comparison, null is considered equivalent to undefined. For precise comparison against null or undefined, it's recommended to use the identity operator: t.origStatus === undefined

Answer №2

It represents the shorthand notation for If-THEN-ELSE, presented as:

  x ? A : B

This syntax signifies "if x is true, then do A; otherwise, do B". For further insight, refer to:

Answer №3

This is a condensed version of an if-statement in programming. For more information, you can check out the MDN conditional operator. In its entirety, your code would be written as follows:

if ( t.origStatus !== undefined && t.status !== t.origStatus && t.statuseffective === null ) {
  errMess = errMess + t.systemname + ": Status effective date invalid.\n";
} else {
  errMess = errMess;
}

Answer №4

  if (t.origStatus !== null && t.status !== t.origStatus && t.statuseffective === undefined)
      errMess =  errMess + t.systemname + ": Invalid status effective date.\n";

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