Javascript one line If...else...else if statement

I know you can set variables with one line if/else statements by doing var variable = (condition) ? (true block) : (else block), but I was wondering if there was a way to put an else if statement in there. Any suggestions would be appreciated, thanks everyone!

Sure, you can do nested ternary operators but they are hard to read.

var variable = (condition) ? (true block) : ((condition2) ? (true block2) : (else block2))

tl;dr

Yes, you can... If a then a, else if b then if c then c(b), else b, else null

a ? a : (b ? (c ? c(b) : b) : null)

a
  ? a
  : b
      ? c
        ? c(b)
        : b
      : null

longer version

Ternary operator ?: used as inline if-else is right associative. In short this means that the rightmost ? gets fed first and it takes exactly one closest operand on the left and two, with a :, on the right.

Practically speaking, consider the following statement (same as above):

a ? a : b ? c ? c(b) : b : null

The rightmost ? gets fed first, so find it and its surrounding three arguments and consecutively expand to the left to another ?.

   a ? a : b ? c ? c(b) : b : null
                 ^                  <---- RTL
1.            |1-?-2----:-3|
             ^ <-
2.        |1-?|--2---------|:-3---|
     ^ <-
3.|1-?-2-:|--3--------------------|

result: a ? a : (b ? (c ? c(b) : b) : null)

This is how computers read it:

> 1. Term a is read.
> Node: a > 2. Nonterminal ? is read.
> Node: a ? > 3. Term a is read.
> Node: a ? a > 4. Nonterminal : is read.
> Node: a ? a : > 5. Term b is read.
> Node: a ? a : b > 6. Nonterminal ? is read, triggering the right-associativity rule. Associativity decides:
> node: a ? a : (b ? > 7. Term c is read.
> Node: a ? a : (b ? c > 8. Nonterminal ? is read, re-applying the right-associativity rule.
> Node: a ? a : (b ? (c ? > 9. Term c(b) is read.
> Node: a ? a : (b ? (c ? c(b) > 10. Nonterminal : is read.
> Node: a ? a : (b ? (c ? c(b) : > 11. Term b is read.
> Node: a ? a : (b ? (c ? c(b) : b > 12. Nonterminal : is read. The ternary operator ?: from previous scope is satisfied and the scope is closed.
> Node: a ? a : (b ? (c ? c(b) : b) : > 13. Term null is read.
> Node: a ? a : (b ? (c ? c(b) : b) : null > 14. No tokens to read. Close remaining open parenthesis.
> #Result is: a ? a : (b ? (c ? c(b) : b) : null)

Better readability

The ugly oneliner from above could (and should) be rewritten for readability as:
(Note that the indentation does not implicitly define correct closures as brackets () do.)

a
  ? a
  : b
      ? c
        ? c(b)
        : b
      : null

for example

return a + some_lengthy_variable_name > another_variable
		? "yep"
		: "nop"

More reading

Mozilla: JavaScript Conditional Operator
Wiki: Operator Associativity

---

Bonus: Logical operators

var a = 0 // 1
var b = 20
var c = null // x=> {console.log('b is', x); return true} // return true here!

a
  && a
  || b
      && c
        && c(b) // if this returns false, || b is processed
        || b
      || null

Using logical operators as in this example is ugly and wrong, but this is where they shine...

"Null coalescence"

_{This approach comes with subtle limitations as explained in the link below. For proper solution, see Nullish coalescing in Bonus2.}

function f(mayBeNullOrFalsy) {
  var cantBeNull = mayBeNullOrFalsy || 42                    // "default" value
  var alsoCantBe = mayBeNullOrFalsy ? mayBeNullOrFalsy : 42  // ugly...
  ..
}

Short-circuit evaluation

false && (anything) // is short-circuit evaluated to false.
true || (anything)  // is short-circuit evaluated to true.

Logical operators
Null coalescence
Short-circuit evaluation

---

Bonus2: new in JS

Proper "Nullish coalescing"

developer.mozilla.org~Nullish_coalescing_operator

function f(mayBeNullOrUndefined, another) {
  var cantBeNullOrUndefined = mayBeNullOrUndefined ?? 42
  another ??= 37 // nullish coalescing self-assignment
  another = another ?? 37 // same effect
  ..
}

Optional chaining

Stage 4 finished proposal https://github.com/tc39/proposal-optional-chaining https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining

// before
var street = user.address && user.address.street
// after
var street = user.address?.street

// combined with Nullish coalescing
// before
var street = user.address
  ? user.address.street
  : "N/A"

// after
var street = user.address?.street ?? "N/A"

// arrays
obj.someArray?.[index]

// functions
obj.someMethod?.(args)

In simple words:

var x = (day == "yes") ? "Good Day!" : (day == "no") ? "Good Night!" : "";

This is use mostly for assigning variable, and it uses binomial conditioning eg.

var time = Date().getHours(); // or something

var clockTime = time > 12 ? 'PM' : 'AM' ;

There is no ElseIf, for the sake of development don't use chaining, you can use switch which is much faster if you have multiple conditioning in .js

I know this is an old thread, but thought I'd put my two cents in. Ternary operators are able to be nested in the following fashion:

var variable = conditionA ? valueA : (conditionB ? valueB: (conditionC ? valueC : valueD));

Example:

var answer = value === 'foo' ? 1 :
    (value === 'bar' ? 2 : 
        (value === 'foobar' ? 3 : 0));

if-else:

a = b ? (true block) : (false block)

if-else if-else:

a = b ? (true block) : b = c ? (true block) : (false block)

if:

a = b && (true block)

if-else-if(nested):

a = b ? (true block) : b = c && (true block)

• note think so much, just implement and see the results, where a, b and c is variable

You can chain as much conditions as you want. If you do:

var x = (false)?("1true"):((true)?"2true":"2false");

You will get x="2true"

So it could be expressed as:

var variable = (condition) ? (true block) : ((condition)?(true block):(false block))

  a === "a" ? do something
: a === "b" ? do something
: do something

if i use code like this

const alpha = a ? a : b ? b : c

it will get

> Extract this nested ternary operation into an independent statement.

from so i recommend to use this

const alpha = a || b || c

it works for me