What do the characters of "?" and ":" in JavaScript

Conditional operator (ternary)

Which is a shorter form of the "if else" structure.

For example

var result = 6%2==0 ? "Even" : "Odd";

Is the same as

if(6%2==0){
     result = "Even";
}
else{
     result = "Odd";
}

so in your example

if(self.isUploadable){
    n = fileStack.length;
}
else{
     n = numFiles;
}

That syntax is from JavaScript and corresponds to the ternary operator :

condition ? expression1 : expression2

Examples:

> var mayor = 4 > 5 ? "Si" : "No";
> mayor
"No"
> var mayor = 100000 > 0 ? true : false;
> mayor
true
> var mayor = array1.length > array2.length ? hacerAlgo() : hacerOtraCosa();

Note that in the last example both hacerAlgo()and hacerOtraCosa()should return something that makes sense given the context you're working under.

Since ternary operators are expressions in JavaScript, it's possible to use them like this, for example:

> var masculino = false;
> var saludo = "Hola " + (masculino ? "chico" : "chica") + ", ¿cómo estás?";
> saludo
"Hola chica, ¿cómo estás?"

Its counterpart using the statement if {} else {}would be:

var masculino = false;
var saludo = "Hola ";
if (masculino) {
    saludo += "chico";
} else {
    saludo += "chica";
}
saludo += ", ¿cómo estás?";

Yes, you save a few lines of code.

Answering your questions, ?it simply evaluates the condition on the left and :is simply the separator between the expressions that are evaluated based on the result of the condition.

Note:

Do not confuse ternary operator with the Elvis operator .

If it were the case that it isUploadableis trueonly when it fileStackcontains data, then this would also work for you

n = fileStack.length || numFiles;

Remember that:

• null
• undefined
• false
• 0
• ''(stringempty)

they are falsefor JavaScript.

It is an if else can be used in both javascript and PHP

$variable = ($var_1 == $var_2 )?valor si es cierto:valor si es falso;