Shorthand if/else statement Javascript

Question

I'm wondering if there's a shorter way to write this:

var x = 1;
if(y != undefined) x = y;

I initially tried x = y || 1, but that didn't work. What's the correct way to go about this?

Muttra

x=y||x works if you dont care about strict undefined – Olatha

Answer 1

var x = y !== undefined ? y : 1;

Note that var x = y || 1; would assign 1 for any case where y is falsy (e.g. false, 0, ""), which may be why it "didn't work" for you. Also, if y is a global variable, if it's truly not defined you may run into an error unless you access it as window.y.

---

As vol7ron suggests in the comments, you can also use typeof to avoid the need to refer to global vars as window.<name>:

var x = typeof y != "undefined" ? y : 1;

Backside

Yay for ternary operators. I'll try that out. Edit: Ah, okay. What about 'undefined'? Didn't seem to catch that. – Muttra

What do you mean? The string 'undefined' is a true value, and is not equal to the actual undefined value. – Backside

I meant, where the variable hasn't been declared at all. I know the string 'undefined' evaluates to a boolean true, but that's not what I was looking for. – Muttra

When you say it "didn't seem to catch that", what do you mean? If you're dealing with a global variable that may not be defined, you'd probably want to use window.y (which will actually return undefined) rather than y (which could potentially cause an error). – Backside

I'd initially tried alerting the value of x, but nothing popped up. Further experimentation via console.log showed that y was undefined and it wouldn't even run the || statement. – Muttra

See my edited comment above about using window.y instead of just y. – Backside

Yep, that does the trick; thanks. Still, I'm curious to know why y's undefined didn't evaluate to false and thus lead to x equaling 1. Edit: if I define window as _, I can then say var x = _.y || , which is as short as I could want. I'm only checking to see if y is undefined in this case so I'm not worried about falsy vs. false. – Muttra

-1 — That ternary expression has exactly the same result as x = y || 1, since null, 0 and '' (empty string) are all == undefined. You should use === (if that's what the OP wanted). – Bony

@Bony - Updated to !== on matter of princple. That said, false == undefined is false. Try it (or just look at i.imgur.com/rHXiq.png). – Backside

its probably better to test for definedness using typeof – Basir

@Amber—you have your rep back. – Bony

Answer 2

Another way to write it shortly

bePlanVar = !!((bePlanVar == false));

// is equivalent to

bePlanVar = (bePlanVar == false) ? true : false;

// and 

if (bePlanVar == false) {
    bePlanVar = true;
} else {
    bePlanVar = false;
}

Indicia

Answer 3

y = (y != undefined) ? y : x;

The parenthesis are not necessary, I just add them because I think it's easier to read this way.

Happening

Your parens are unbalanced (and also unecessary). – Backside

@Backside The moment you start using javscript shorthand, you are already saying you dont care about readability, so why bother with balanced parens?. – Galoshes

Answer 4

Other way is using short-circuit:

x = (typeof y !== 'undefined') && y || 1

Although I myself think that ternary is more readable.

Obsecrate

Answer 5

Here is a way to do it that works, but may not be best practise for any language really:

var x,y;
x='something';
y=1;
undefined === y || (x = y);

alternatively

undefined !== y && (x = y);

Olatha

Just noticed that this was already supplied by @AndreFigueiredo – Olatha

Not exactly the same, thank you for your answer, though generally it's not good practice assign value in a condition. – Obsecrate

Answer 6

Appears you are having 'y' default to 1: An arrow function would be useful in 2020:

let x = (y = 1) => //insert operation with y here

Let 'x' be a function where 'y' is a parameter which would be assigned a default to '1' if it is some null or undefined value, then return some operation with y.

Purifoy

This is not what OP was asking for. You're suggesting that x becomes a function unless you immediately invoke that. Even then, this makes the code overly complex, since in JavaScript, default assignments can just be expressed with the || operator as @Olatha commented in OP or with the ternary operator in accepted answer – Topliffe

Answer 7

You can try if/else this shorthand method:

// Syntax
if condition || else condition

// Example
let oldStr = "";
let newStr = oldStr || "Updated Value";
console.log(newStr); // Updated Value

// Example 2
let num1 = 2;
let num2 = num1 || 3;
console.log(num2);  // 2  cause num1 is a truthy

Thermosiphon