regex - regexp pattern to match alphanumeric strings without initial spaces -

i have input pattern setted this: pattern="[a-za-z0-9]+"

when type space in input, returns me error message ( ).

but, when type mi full name, e.g. jhonatan sandoval, too.

how can sett pattern no spaces before name?

that work expect:

pattern="[a-za-z0-9][a-za-z0-9 ]+"