I've recently been given this piece of javascript (as part of a jQuery function)...
var h = "innerHeight" in window ? window.innerHeight : document.documentElement.offsetHeight;
var w = "innerWidth" in window ? window.innerWidth : document.documentElement.offsetWidth;
I've never seen "innerHeight" in used before, and I cannot find any explanation of what it is for, or why it's used. (Doing a Google search for the word in isn't exactly helpful.)
Is it jQuery syntax?
No, the in operator is core JavaScript.
It resolves as true if the object on the right hand side has a property with a name that matches the string on the left hand side.
See a simple example:
var foo = {
a: 1,
b: undefined
}
var o = document.getElementById('output');
o.innerHTML = ("a" in foo) + "<br>" +
("b" in foo) + "<br>" +
("c" in foo) + "<br>";
This is pure JS.
This is similar to object.property with a little difference.
object.property will fail in cases property is not set and also in cases it has been set to some false value, e.g. undefined, null, 0 etc
property in object is slightly better because it doesn't looks for its value.
Check if a object's property exists.
in is used to check if an object contains a specific property , this is rappresented by a string.
var obj={a:1,b:2}
// in
console.log('a' in obj); // true
console.log('c' in obj); // false
Said that.. there is a faster/shorter way to do that.
// this does not work if the property's value is 0,null,undefined,false...
console.log(!!obj.a); // true
console.log(!!obj.c); // false
demo
in your case a better solution would be:
var H=window.innerHeight?window.innerHeight:document.documentElement.offsetHeight
or even better :
var H=window.innerHeight||document.documentElement.offsetHeight
Theoretically window.innerHeight could be 0 , so at that point it would try to get the document.documentElement.offsetHeight whitch returns undefined and you should add another or ||0 to return 0 and not undefined. But that does not happen ;).
Putting window.innerHeight in front of document.documentElement.offsetHeight accelerates the check as window.innerHeight is standard, so there is a higher chance that it's the correct choice.
You can see it as if innerHeight <inside> window then window....
inside term means?