mjhjmtu

None of my newcommand declarations work for hspace, with or without arguments; I use the latest MathJax with the general libraries. Attempts so far:

newcommandhs[1]hspace#1
newcommandhs[1]hspace#1
newcommandhs[1]hspace#1px
newcommandhs1hspace10px

I have a pageful of other newcommand declarations that work just fine, unsure what's failing here. Any remedy?

In usual conditions, all commands in TeX must be preceded by a backslash, to tell TeX that they are commands, so instead of

newcommandhs[1]hspace#1

you need

newcommandhs[1]hspace#1

which will work as you expect.

Side note: If you just want to create a copy of a command with another name, you can use let: leths=hspace. With the newcommand approach the hs command will use hspace, and with the let approach it will be a copy of hspace. One advantage of the latter is that hs*argument will work as you'd expect. With newcommand it won't.

The second version adds an extra pair of braces that shouldn't be there, so it won't work as well.

hspace1cm will expand to hskip#1relax, which isn't valid syntax and will throw you a Missing number error.

The third version is the same. The unit will only appear after the Missing number error, so it is of no use there. Besides, TeX doesn't know the unit px, so even if you remove the braces you'll still get a Illegal unit of measure.

The fourth contains, besides the illegal px unit, two problems. The first is that in usual circumstances numbers aren't allowed in command names, so you can't use hs1. The second is that the first optional argument of newcommand (the number of arguments) must not be empty (). An empty argument is very different from a missing argument! If you try to do that (after removing the number from the command name) you'll get another Missing number error because LaTeX was expecting a number there.