Why does the space bar do page down in browsers
Why is the space bar doing a page down in some viewer apps, especially browsers and PDF readers?
For me this seems to be a bit counter-intuitive, and also this behaviour affects games and other interactive HTML5 apps, because if you map some action to the space bar it might also scroll down the page, which is not what you want. Also the arrow keys, page down button and the mouse scrollwheel are usually enough options to scroll down the page.
Are there any historical or usability reasons for this behaviour?
It's also a usability issue for non-full-screen videos. Space is frequently used to pause/play videos; I'm always scrolling down youtube thanks to this.
Me neither ! - and I've been using a browser since Netscape Navigator 1.0. The spacebar is for adding spaces in my mental model of the world...
None of all that gobbledegook above means anything. Every time I hit the spacebar in Notability, it takes me backwards to a list of my documents. No one at Apple Care or elsewhere knows how to solve the problem. So my answer here is just as good (or bad) as all those above, which also didn't help. I believe there is no solution for this.
The historical reason is that that's what the spacebar does in more, the lowest common demoninator (and probably oldest) of text pagers. In
more, it makes sense to map the largest key on the keyboard to the most common action: show the next page.
In the glory days of
more, you couldn't count on mouse scrollwheels, page down buttons, or sometimes even arrow keys.
moredoesn't even have a "page up" feature (you can't go back).
Although in the text-based world
morehas mostly been replaced with more powerful pagers like less (which can move backward), that spacebar convention remains, and has even migrated to the GUI world.
i think in this case it's size and position contributes to the choice of this functionality, like it does with stop and play on youtube
Do you _guess_ the historical reason or do you _know_ it? Could you provide some evidence?
"Press space to continue" was a very common way to move through an app in the pre-GUI home computing days of the 1980s, probably because it was the biggest button. Some apps implemented "Press any key to continue". This was slightly risky, as it didn't really mean "any" key, pressing escape or break would probably exit the programme, and it's alleged that some people couldn't find the "any" key.
@phresnel The request for evidence is not unreasonable, but do remember that some of us are old enough that our programming days predate the PC and we've *lived* this 'spacebar for page down' time. There are probably many things not being written down (to be *evidence* later) because they're so obvious. For me, Celada's answer is that obvious. :)
@Cheeseminer: Alternatively, the formulation could be changed to no longer represent a fact. If something cannot be proven then it can at most be a claim. There's definitely a correlation, however, obviousness is the enemey of the truth. Example: To me it is obvious that the earth is flat and that the sun sets and rises around our planet. Air is immaterial, because I cannot hold it. And there is no mass market for computers, so probably you are working at IBM and currently computing the diameter of the earth disk.
Other examples backing this hypothesis: slash shortcut for find in Firefox (from vi), ctrl+a / ctrl+e as Home and End on MacOs (from emacs)... I guess programmers (which are the first users of these programs) enable shortcuts compliant with their previous habits.
@phresnel I think the hard evidence you are looking for simply doesn't exist. This behavior of the space bar organically took root over time and eventually became tradition. It's often hard to pinpoint a specific decision; the best you might be able to do is ask Daniel Halbert, author of `more`) why he chose the spacebar, and even that relies on the presumption that `more` drove that choice. Sometimes the best we can do is theorize and present evidence that *supports* our theories.
@phresnel (continued) ... This sort of thing comes up a lot in UI/UX design. Why is the minimize button on the top right? Why do pixel-based Windows dialogs use a 6 pixel button spacing and 12 pixel borders.aspx) (and similarly, why are DLUs based on 8-point MS Sans Serif)? Why is does Ctrl+V mean paste (it was chosen by Xerox Parc back in Alto days but good luck finding a rationale)? At some point, somebody made a decision, possibly for completely arbitrary reasons, and it stuck.
@Jason C: Yeah, of course, I do not disagree with all the comments. But this confirms that it should not be represented as a fact, but as a guess or something that is probable.
@phresnel: Not really, in human communication and the english language indicative mood can be used to express opinions ("You look gorgeous!") or things one believes to be true. SE is *not* a encyclopedia, but a Q&A network where *humans* give answers. Any answer is a claim, no matter the mood in which it is formulated. Citing any sources - which will be dubious at best here at UX - won't change that. Or do you wish that on mathematics SE users would answer the question "What is 1+1" with "I, and person x & y, claim that the answer is 2"? That would just ruin efficient communication.